Jul 262019
Volvo Penta MDI Black Box Overview

Last Updated on 06 July 2020 by Eric Bretscher

In this article, we have a look at the Volvo Penta MDI electronic black box while relocating it off the side of a Volvo Penta D2-40B engine in order to protect it from the heat and vibrations.

IF YOU OWN A FAILED MDI BOX, PLEASE CONSIDER SENDING US PHOTOS OF THE INSIDE AFTER LIFTING THE LID! There have been many revisions of the module and it would be extremely interesting to see what design changes were made.


Volvo Penta began the release of the current D-Series marine diesel engines around 2006. While all the larger models are common-rail, fuel injected electronic engines, the smaller D1- and D2-series engines, up to 4 cylinders and 75HP, still operate with traditional mechanical injection pumps. Volvo elected to interface these engines to its electronic gauges and controls by using an electronic interface module: the MDI (Mechanical Diesel Interface) black box. For some owners at least, the MDI box rapidly gained fame as the least reliable part of an otherwise excellent engine.

Volvo Penta MDI Black Box Overview

The Volvo Penta MDI black box once separated from the engine and most of the wiring harness.

The MDI box has had a surprisingly long revision history over the years, aimed at addressing failure modes and on-going reliability issues, with some versions recording high failure rates. The table below, compiled from publicly available information, shows the consecutive model numbers and approximate year of release when it could be determined.

Volvo Part Number Year released
3843668 2006
21120710 2008
21558929 2014
22458451-P 2017
23195776 2018
23231607: kit containing 23195776? 2019


Volvo Penta MDI Box P/N 21558929

By 2014, a 15A blade fuse was added to the MDI box, protected by a sealed rubber cover.


The role of the MDI box is largely a supervisory one in the sense that it reads all the engine sensors and outputs the information over CANbus for the Volvo EVC gauge/display system, but it does have a minor control function: it switches the engine glow plugs, the starter motor solenoid, the fuel stop solenoid and it energises the alternator about one second after the engine has started. A failure of the MDI box leaves the engine dead, but it can be bypassed very easily to preheat and start using a simple jumper cable or even a screwdriver, with caution. The key issue is the lack of monitoring over coolant temperature and oil pressure afterwards. In fact, should the concern of being unable to start the engine be acute enough, one could opt to install an independent parallel engine start circuit by adding two external relays to connect the “PREHEAT” and “START” terminals to the “BATT” terminal at the push of a button. In this case, the preheating relay must be able to handle a current of about 10A per glow plug, so 40A on a 4-cylinder engine. Briefly applying power to the “D” terminal post of the alternator after the engine has started will cause it to begin charging normally, but increasing RPMs can be enough to achieve the same, due to the residual magnetism normally present in the rotor.

Reliability Factors: Heat and Vibration

The MDI box is factory-mounted to the side of the water-cooled exhaust manifold. When the engine has been running for some time, its temperature is approximately equal to that of the coolant: too hot to keep a hand on. Furthermore, it is hard-mounted to the manifold casting and fully exposed to the vibrations of the engine.

Volvo Penta D2-40 Factory Engine

Volvo Penta D2-40 engine in its factory configuration with the MDI black box attached to the water-cooled exhaust manifold. Note that this photo shows no extra length in the wiring harness to the MDI box.

High heat and vibrations are two well-known root causes of premature failure for electronics. Fortunately, I make little use of the engine and I very rarely run it for any amount of time. This may be why I never experienced any issues with my MDI box in 10 years and 230 engine hours. Nevertheless, I always had in mind to relocate it off the engine block to prevent a failure.

Relocating the MDI Box off the Engine Block

A preliminary investigation some time ago had shown that the wiring harness connecting the sensors around the engine to the MDI box was generally long enough to allow remote-mounting the box on the sidewall of the engine compartment, thanks to some extra length in the loom bundled with plastic cable ties. In fact, this extra length almost suggested that relocating the MDI box off the engine had been made possible and favoured by design, at least on early engines. This didn’t come as a complete surprise as it was not the first instance I found of understated, unadvertised superior engineering on a Volvo Penta engine. Another one is remote voltage sensing for the alternator. I would have otherwise extended the cabling by cutting it and splicing it.

Volvo Penta D2-40 engine with MDI black box relocated off the engine

Volvo Penta D2-40 engine with MDI black box relocated off the engine to protect it from the heat and vibrations.

I constructed a plywood pad fitted with two M6 studs and epoxy-glued it to the sidewall of the engine compartment to support the MDI box. I also had to accommodate a few other constraints, namely the lengths of the Multilink cable feeding the EVI gauges and the cable to the EVI control panel, as well as the presence of an access panel immediately to the side of the engine. I moved the MDI box down and back to a location close to the rear engine mount, quite low. A low location may be more prone to see water in a rare and improbable event, but it is likely to be cooler too and I decided this would be adequate. I only had to lengthen the coolant temperature sensor wire and I was otherwise able to re-route the loom without issues.

Reliability Factors: Electrical

Many failures, and especially short-term failures, instead have electrical root causes except for some rare instances where engines shipped with clearly defective MDI modules. Some early versions would have failed from exposure to the back EMF of the engine stop solenoid. This can be prevented by adding a diode over the device to short the negative spike out and this is an electrical alteration I will carry out at some point (or I will trace the wiring and add it within the module if not already there).

Many failures of the module, reported or real, have in fact been caused by poor connections to the battery: a high resistance path causes the voltage to drop whenever the starter solenoid and motor are energised, which can easily cause the electronics to reset and lead to starting problems. A negative voltage spike is also induced into the engine electrical system each time at the end of cranking. It normally has very little effect because the very low impedance of the battery absorbs it, but if the battery is poorly connected, it can cause high reverse voltages to appear at the MDI box supply. This event has demonstrably killed many modules, often several in succession, with the blame usually going towards the black box and Volvo Penta, when it is in fact an installation problem. Use batteries with threaded studs and quality disconnect switches and ensure that all the connections are bolted tight.

Don’t even think about replacing the module until the path to the battery is above any suspicion

It also pays to remember that, in the factory configuration, the alternator charges into the main positive supply terminal at the starter solenoid. Anything less than a solid, uninterrupted connection of the engine to the battery while the alternator is charging will cause the voltage of the engine electrical system to spike up with the risk of destroying the MDI module.

Some modules were also lost due to the addition of ground disconnect relays to the installation on alloy boats because of the unclamped back EMF of the relay coil. 

Pathways Following an MDI Box Failure

In the light of the poor reputation of the Volvo Penta MDI black box, I always wondered what I would actually do if I faced such a failure, remembering that both reliability and maintainability are important to me in the context of ocean cruising in remote places. I envisioned a few pathways, listed below in decreasing order of desirability:

  1. Repairing the module, if possible. With an electronic engineering background, this is always the first consideration that comes to mind, but the electronics could be potted in resin and completely inaccessible. The root cause of the failure, once identified, should be addressed however.
  2. Doing away with the Volvo Penta EVI instruments system once and for good. This would require installing standard automotive gauges for coolant temperature, oil pressure and engine speed, as well as a few stand-alone switches and relays to deal with the glow plugs, starter and electric stop.
  3. Developing an equivalent replacement module. This would represent more work, but a better third-party open-source module would clearly have a market. Rather than using gauges on CANbus, a simple LCD display could present all the information. Such a module could be much simpler than the Volvo MDI box, which is clearly inheriting technology from the ECUs of the larger electronic engines in the range.
  4. Replacing the module. It is easy (and quite costly), but I have heard reports of people having gone through more than one module, because replacement alone obviously failed to address the root cause. This would hardly be satisfactory.

The second option has always been highly desirable in my eyes, because it would replace a proprietary system with one that is standard and fully maintainable at low cost more or less anywhere in the world. The field of engine instrumentation seems to be split between European and American standards. Here, any such solution would rely on European gauges and the key challenge could be identifying the factory-installed sensors to select compatible gauges. Worst case, some of the sensors could require replacement to ensure compatibility.

Would the Volvo Penta MDI Box Be Repairable?

While I had the MDI box off the engine and well accessible, I couldn’t resist investigating to what extent a failure would be repairable for my own forward planning; this hinged upon whether the electronics inside were encapsulated or not. I started by unplugging all the multicore cables to facilitate handling, but I left the three bolted heavy wires in place. The housing is made out of aluminium, but the baseplate accepting the connectors is moulded black plastic, held in place by four Torx T-10 screws. A compression rubber seal is present between the two parts. Removing the screws presented no difficulty and then the aluminium cover separated effortlessly.

Underside of the Volvo Penta MDI Black Box

The underside of the Volvo Penta MDI black box reveals three sockets for Deutsch sealed connectors and terminal posts for the battery supply and cables to the glow plugs and the starter motor solenoid. This baseplate is held in place by four Torx T-10 screws.

Underneath the cover, I was very pleased to discover two stacked circuit boards and no potting compound whatsoever. The fully sealed nature of the enclosure also means that the circuit boards are not coated and could be easily worked on if necessary. The top board contains two 40A-rated relays switching the preheat circuit and the starter solenoid. It also includes the power supply for the electronics and additional circuitry with a IRF4905 P-channel MOSFET transistor likely related to the alternator D+ connection, but I didn’t formally trace this. The supply for the logic circuits appears to originate from a NCV4269 5-volt linear regulator, which can handle spikes of up to 60V and reverse voltages down to -40V. The key point of interest here is two electrolytic capacitors rated 220μF / 63V in the power supply section, because these components are well-known to age faster and fail early when exposed to heat. This would make them prime suspects in case of black box failure, because a degradation of these capacitors would result in poor filtering of the electrical noise from the alternator and this could ultimately affect voltage regulation and the operation of the CPU. Here, the capacitors appeared in good condition, without signs of swelling or electrolyte leakage. As far as components go, everything else in the design of the MDI module should generally prove quite durable and resilient. The other enemy of electronics is vibrations and, here, in the absence of encapsulation, some of the larger components in particular could be prone to cracking of the solder joints over time.

Internal view of the Volvo Penta MDI Black Box

Removing the lid of the Volvo Penta MDI black box reveals two stacked circuit boards. The top board contains relays and transistors for power switching, as well as the power supply section with two electrolytic capacitors and a 5V regulator.

The bottom circuit board is the control board, which communicates with the upper board through a 12-pin pluggable header arrangement. While I didn’t attempt a complete teardown of the MDI box, it seems that separating and extracting the top board should be quite easy after disconnecting the three heavy-current terminal posts. This would give access to the solder points to replace the capacitors or even the relays if it ever proved necessary.

Volvo Penta MDI Black Box Stacked PCB Construction

The heavy current terminal posts on the left connect directly to the switching board. The control board is hidden underneath it with the CPU and crystal oscillator well visible near its edges.

The bottom circuit board carries the CPU and crystal as well as more interfacing components to deal with the sensor signals and the CANbus interface to the gauges. The pins engaging into the sealed Deutsch connectors of the MDI box are soldered to it and they should be expected to just pull through the plastic baseplate, same for the auxiliary flat blade terminals. The control board may be less likely to require repairs, but it is not impossible of course. Not dismantling the module only affords a limited view of the circuit. The Philips / NXP-branded CPU is a LPC2119 microcontroller with 64kB of flash memory, quite a powerful 32-bit processor built on an ARM7 core with 2 CANbus interfaces and a fast 10-bit analog/digital converter. The crystal frequency was not readable.

Volvo Penta MDI Black Box CPU

The CPU used in the Volvo Penta MDI black box is a LPC2119 microcontroller with 64kB of flash memory.


While I took a while before finally relocating the MDI black box off the side of the engine, it should clearly be the first thing done when installing these engines. The presence of electrolytic capacitors in the module looks like a recipe for trouble, even though such capacitors can technically be rated for service lives in the thousands of hours at the temperatures considered. In all cases, the combined exposure to vibrations and thermal stresses promotes the breaking of solder joints over time.

Fortunately, the construction of the MDI box allows access to the electronics. Component replacement or even reflowing the solder over the boards appears perfectly achievable, so a failed module could be repaired. If this was not successful, a replacement module should arguably be able to offer a long service life, provided it is installed in a protected location. The fact that the electronics are not encapsulated makes them both repairable and more vulnerable to failure from exposure to vibrations.

In case of failure, replacing the whole Volvo Penta EVI monitoring system with conventional gauges may not be more costly (in terms of materials) than replacing the MDI black box and doing so would eliminate any reliability issues once and forever. This is a pathway I would seriously consider if I happened to be unable to repair a failed module.

  71 Responses to “Engine Reliability: A Look at the Volvo Penta MDI Black Box”

  1. Thank you for this interesting and informative article.

    On my D2-75F, the +12V power supply to the MDI is sourced from the starter motor rather than from the battery. This would seem to make the unit vulnerable to voltage transients owing to the inductance of the starter motor. When you looked within the MDI, did there appear to be adequate protection in the MDI box against such transients?

  2. Dear Jeremy,

    As the only supply from the battery is terminated at the starter motor solenoid, this is likely to be valid for all the engines using the MDI module.

    Looking at some of the key components like the NCV4269 linear voltage regulator producing the 5VDC supply, and the 63V-rated filter capacitors, the module seems to have been designed around a 60V peak supply voltage limit. A number of other parts I identified had higher voltage ratings. I didn’t find any large capacity transient voltage suppressors anywhere, so it seems quite clear that Volvo opted to design for a sufficiently high peak voltage and I also think it is the most robust option in this context. 60V should be ample considering that the cables to the battery are normally both quite short and substantial. Longer and/or undersized cables could allow the voltage to spike more at the engine, but even then the available margin seems quite considerable.

    One potential scenario that could lead to the electrical destruction the MDI box is an alternator load dump caused by the loss of the battery while charging at high current. In this case, the surge could easily exceed 60V, especially with the standard Volvo wiring which also connects the alternator output (B+) to the started motor solenoid.
    In most cases, it makes sense to run a new dedicated heavy cable from the alternator B+ post to the battery, or – better – to a battery isolator for charging separate banks. This normally mitigates or even entirely eliminates this possibility.

    Kind regards,


  3. Great ideas about the MDI box, thanks!
    The LCD panel on the MDI Panel Tach module (VP p/n 21628160) on my VP D1-30B has failed. I would like to replace just the LCD module a la the old VDO tachs but am having a very hard time finding any reference to source the part. Can you help?

  4. Hello Royce,

    The link between the MDI box and the EVC tachometer (Volvo Penta Multilink cable) uses the J/1939 automotive protocol over CANbus. It should generally be possible to replace the EVC tachometer with a generic J/1939 engine data display (search for J1939 display). Another way is bridging the data to NMEA2000 and display it with other marine data, but this is more suitable for vessels already using a NMEA2000 instrument system.

    You can find information about bridging and the messages used by the Volvo Penta EVC engines (to assess display compatibility) here: https://www.yachtd.com/news/j1939_volvo_penta_evc_gateway.html.

    Kind regards,


  5. Thanks for the article, I am on my Third MDI, Two were replaced by the previous owner and 1 by me and I only have a total of 150 hours on the Volvo Penta 55s. I like the idea of relocating the MDIs away from the Engine and will look into the feasibility on my boat.
    You did mention the ability in a crisis to bypass the MDI as my Windlass would not work without the Starboard Engine I would be very interested in learning how to do that.

    • Stephen,

      The article does describe how to start the engine without the MDI module: make an external connection between the “BATT” post and “PREHEAT” or “START” on the MDI box to respectively preheat and crank the engine.

      Make sure all your windlass wiring originates from the battery and doesn’t under any circumstance go to the engine or share any current path with the engine cables. Each time you stop the windlass motor, a voltage spike is produced and it is essential that it is routed back directly to the battery where it can be absorbed.

      Best regards,


  6. Hello

    after just 18h (8 quick sea trails and tests) of running our D2-60 the MDI box had to be replaced by Volvo. Do think in this short time the capacitors really could be a source of troubles? In our case it must be another “source of pain”. What do you think
    Best regards

    • Hello Lorenzo,

      Clearly not, capacitor failure is a long-term ageing issue. Electronics are most likely to fail either in very early life (component or assembly defects) or from age-related problem after a duration depending on the environmental conditions.

      I wouldn’t worry about it unless the replacement one also fails in short order, except if there is something unusual/abnormal in the wiring of your engine. Some people have reported MDI box failures in relation with ground-disconnect relays that were added into the standard wiring on metal boats. Electrically insulating the whole engine from the hull is a far more sensible and effective approach in this case…

      Best regards,


  7. Hi Eric,
    Interesting article, thanks!
    I have a 2006
    Volvo Penta D2-55-C
    It has the simple panel with tach, LCD engine hours (not working) and key on/off, the key also controls the glow plugs. The engine has a black box on the coolant side like the one in the picture. What I would like to do is get the engine data, RPM, temp, oil pressure to my iPad. Do I need to buy a penta MDI interface to do that? I have NMEA 2000 on the boat too.

    • Hello Mike,

      You need a gateway to bridge from the J/1939 protocol used by Volvo Penta to NMEA2K. There are aftermarket devices to do that, like the one made by Yacht Devices (please note that I have never used or seen it however). Have a look and see what you can find.

      Best regards,


  8. My understanding is that the MDI module also controls the alternator output – no battery charge if bypassed. Is there a fix for this.

    • Hello Murray,

      It is incorrect. The alternator is a standard alternator and it charges independently of the MDI module. The only thing the MDI module does is kick-start it about 1 second after the engine fires up. It does this by applying power to the D+ terminal of the alternator (where the charging light is traditionally connected).
      An alternator that has been in service for a while normally has some residual magnetism in the rotor and will often self-excite and start charging by itself if you rev it up high enough.
      However, a simple work-around for this is briefly applying battery voltage to the D+ terminal of the alternator and it will cause the alternator to excite and start charging. The D+ terminal is a small threaded stud with one black wire attached to it and there is a “D” embossed in the backshell casting near it.

      You have raised an interesting point, so I will have a look back at the text of the article and see if the matter should be mentioned there.

      Thanks and kind regards,


      • Great post, thanks!

        My D2-40 (from 2019 with 300 hours) blackbox failed yesterday after an dieselfilter/oilchange where I had to use many long attempts to get the engine running afterwards. Suddenly the panel went all black. I bypassed with an external startbutton and got it running. But my batteries would not charge what so ever, even after high rpms (2500).

        So in my case the blackbox seemes to have to be working to start charging. What can be done to start the charging having bypassed the black box?

        Regards Erik

        • Hello Erik,

          You need to purge the fuel system from air bubbles after a filter change using the manual priming pump located on top of the secondary fuel filter before restarting, otherwise air will get to the injection pump and you might have to purge the injector lines.

          Your case is interesting as you clearly killed your MDI box with the electrical transients generated by switching the solenoid/starter motor. Can you please post or e-mail me the Volvo Penta part number printed on it?

          Anyway, the MDI box energises the D+ terminal on the alternator about 1 second after starting the engine to cause it to start charging. It is the small threaded stud with a single black wire attached to it. Just touch it with a wire at battery voltage and it will start charging immediately. If you are going to do away with the MDI box, then install a charging light (2W incandescent bulb typically, or a power resistor) between the engine “ignition” circuit and this terminal. The light will glow before the engine starts and go out as the alternator starts producing a voltage.

          Kind regards,


          • Thanks for replying!
            Today I got a new MDI box and installed it. After many attemps I got light to the LED display, and engine started. After a minute the battery symbol and alarm came on. I stopped and started and alarm came on again. The alternator was charging so its clearly a false alarm for some reason. Then I reved the engine to 1500 rpms and the temp and rpm gauges died, came back on and froze, and the display died. And that was it. No more life. Had to kill engine manually. Do you have any idea whats wrong? Some kind of electrical failure/overload/grounding fault into the MDI?

            I’ll mail you the number for both MDI

            • Hello Erik,

              I am quite concerned by your observations. The display should come on as you power up the EVC system and, if it doesn’t, it suggests a power supply issue like a bad electrical connection and the prime candidate is the cabling between the battery and the engine, or plugs not fully inserted into the MDI module.
              Also note that the MDI module has two identical sockets labelled “Panel” and “Multilink”, which are physically interchangeable, but incompatible. I remember reading a report that swapping these plugs by mistake damaged the module.
              I would find it very difficult to believe that Volvo shipped a new MDI module that would not readily power up and initialise the display properly.

              When the alternator starts charging, the stator windings feed an AC voltage to the rectifiers connected to B+ and B-. A small secondary rectifier “duplicates” B+ on the D+ terminal to create a supply point that is only on when the alternator is charging (unlike B+ which is normally at battery voltage all the time). D+ is used to power the internal regulator and this means that the alternator remains dead until external power has been applied to D+ and then it produces its own.
              The MDI box applies power to D+ after the engine starts, and then checks periodically that there is voltage on D+ to confirm that the alternator is running. You get a charging alarm if D+ has low voltage, but also if the system voltage exceeds a threshold (around 15V from memory).

              The system died when you increased the alternator RPMs and this can only mean high voltage. There are two possible scenarios: either you damaged the alternator regulator when you were cranking and trying to restart the engine after the filter change, or you are sensing the charge voltage at the battery with the alternator and there is a bad connection in the positive between the engine and the battery. Electrical damage from transients from cranking should not be able to happen if the battery cabling is heavy and the connections are good, so I suspect something is not right there. This would also explain issues with powering up the EVC system and the MDI box failed as a consequence of something else, not in itself.

              It was a mistake to start the engine when things were not powering up and behaving properly in the first place, because if there are such issues, starting the engine is not going to help. If you are lucky, the MDI module will have protected the EVC gauges.

              This would not be the first time I hear about repeated failures of the MDI box because of a bad battery connection. In one instance, the battery disconnect switch was eventually found to be faulty.

              Kind regards,


  9. Hello Eric. Thank you for all your research and commentary. I own a couple D1-30F engines on a catamaran sailboat. I was part of the engine recall program. Since February 2018, I have replaced 5 MDI boxes between the two engines. The first failure didn’t make 2 minutes. Outside of the obvious concerns I’m wondering why VP engineering has not resolved the matter. Beyond them? Your article mentioned vibration and temp issues. My original engines since 2009 had accumulated 880 hours and ran flawlessly with no MDI issues. I think whatever they did electrically
    to bring the new engines into compliance has generated the issue. I’m not an electronic engineer but I believe there’s a sequencing issue that they can’t overcome without a broader look at components in the system all the way to ground. They’ve tried to put a bandaid on this issue since day one. Nobody’s screaming at this moment because they’ve been very generous with replacement parts. But that doesn’t speak to the known defect and safety issue of engine shutdown on waterways or oceans.

    I did read a commentary from someone that indicated that a technician told him that they are stressed over 13.8 volts so essentially any craft with mppt charging might be suspect as to cause of failure. Of course, as the writer indicated, it would be difficult for VP to get around their generator output of 14.2-14.3 volts. So essentially, mppt charging systems with equalizing voltages would void your warranty if that were true. Hmmmmmm…. now there’s a new twist for VP owners and long term boating. Maybe we all ought’a get ourselves some buck converters and jump in.

    So thanks again Eric and if you come up with an engineered fix, please share.

    • Hello KJ,

      There is no doubt that a number of the failures experienced by people, and especially the short-term ones, have had an electrical root cause, rather than premature ageing due to heat and vibrations. My point here is that an electrically sound unit will have a reduced life expectancy if it is left installed on the engine block itself.

      I don’t believe for a second the tale about the 13.8V voltage limit. Not only it makes no sense, but it is idiotic when you consider it from a component rating and electronic design point of view. I know that the back EMF from the fuel cut-off solenoid when the engine is stopped has been blamed to cause failures at sme point and this would have been corrected (by adding a free-wheeling diode obviously). Other failures have been related to “unexpected” installation practices using contactors to disconnect the engine ground when it stops etc. This can cause a negative voltage spike in the engine electrical system. Failures of the mechanical relays were also occasionally reported, but this seemed uncommon and it is trivial to fix. Any disconnection of the battery while the engine is running would almost certainly take out the MDI box before even damaging the alternator and this may have happened in some cases with bad battery switches.
      I have been considering adding a free-wheeling diode to the fuel stop solenoid because it can’t do any harm, but it is generally difficult to propose any improvements to the electronics, because there are so many versions of them and the differences between them are obscure. I wish I had an opportunity to open and inspect the latest model, assuming they haven’t potted the PCBs in resin by now.

      Some revisions of the MDI black box proved to be worse than the versions they were supposed to replace and led to yet another hardware revision. I am also puzzled by the fact that Volvo Penta have been struggling with this issue for that long considering that we had reliable engine control modules (ECM) before these D-Series engines were even brought to the market, but these are not constructed like the MDI black box.

      Remember also that the MDI box has zero control over the operation of the engine itself once it is running. On these engines, emissions control and regulatory compliance are entirely met by the mechanical injection system and thermostat. The only driver behind the many revisions of the module has been reliability.

      Kind regards,


  10. Hello,

    Thank for posting a very interesting article. I have one of the latest versions of the MDI, replaced as a part of the recall campaign in the autumn 2018 at the time I bought the D2-40F. This engine has been working flawlessly for 65h, but now the preheating fails. I have not yet opened the MDI but will do so, and if necessary replace the relay (or add an external relay activated by a manual push-button and / or timer circuit). As far as I can see there are no potting in my MDI. Regarding heat as a root cause of the failures, I added a fan to the engine compartment last year since the generator seemed to become too hot (+90C?) during warm summer days after about an hour of running the engine, the MDI certainly got even warmer.

    Jens in Sweden

    • Hello Jens,

      Thank you for commenting on the build of recent MDI modules. The preheat circuit is extremely simple. If the relay failed after such a short time, it could be vibration-related as it is a mechanical component with a spring-loaded contact and plain bad luck. If they still use the same relay (Song Chuan 822E-1A, 12V coil), then it is available from Mouser Electronics for a few dollars under part number 893-822E-1AS12VDC. Please do send photos of the inside of the new module and the PCBs when you get in there.

      The MDI module is mounted alongside the cylinders below the water-cooled exhaust manifold, which is one of the hottest parts of the engine block and a lot of the heat flows into it by conduction. The new D-Series engines also run hotter than the older models in order to achieve cleaner combustion.

      Kind regards,


  11. Hello Eric,

    The design has indeed been revised: now the use solid-state relays / FET:s only, I will email a photo. I cannot find any bad solder points or obvious signs of damage or ageing. Possibly I will check if the preheat FET receives a gate voltage or not, and in that case I might replace the FET.


  12. I have one of these in my boat. Part number 21558929. It has worled flawlessy for several years. One spring, after been on the hard for a whole season, the fuel was contaminated with water. That resulted in water in the fuel/injection system, causing sudden stop of the engine after just a minute. Didn’t know at that point it was water, not just air in the fuel lines. Probably the diesel in the fuel lines was ok, but when the engine sucked in the contaminated diesel it stopped. Then we suspected that water was the culprit. Emptying all the fuel, cleaned the fuel container/tank, fuel filter and refueled with fresh diesel. Bleed the fuel system, but still no start. It was probably still water in the fuel lines. Managed to get the water out of the system eventually. But in the process we accidently shorted the glow plug rail to ground. That caused a spark and the preheat / glow to not function anymore. The rest, instruments and starting was normal.
    When inspecting the MDI box I encountered that one of the MOSfets didn’t measured the same as the three other. Ordered one new MOSfet (011N04L) and swapped it. It was difficult to desolder with just a soldering iron. In the process the soldering iron slipped and I ripped one SMD capacitor out of the circuit board. It seemed to have survived, as there was no destroyed traces and the capacitor also seemed ok. So I resoldered it.
    But my soldering skills isn’t as good as I wished it was. At close inspection I saw a solder ball betwen the legs of the MOSfet, but as it was at the earth plane, and five of six legs where connected to gether anyway, I didn’t try to resolder. I probably should…
    When connecting the box and all the wiring, we tried to start. That didn’t went well. The system alarmed instantly. And the glow plug rail showed 13 volt. Wich it shouldn’t have, as we haven’t pushed the preheat button yet. In just seconds I smelled burnt electronics (never good) and when I touched the MOSfet it was very hot. I measured it again, and now it was shorted.
    I ordered two new MOSfets from Digi-key (fast shipping, just two days from US to Norway). I resoldered the new one, and now it measured the same as the three other.
    Connected all together, but this time without connecting the preheat lead (the orange one). Turned on the main circuit, no smells. Turned on the display, and all seemed just fine. Still no smell. Shut it down after a few seconds without trying to neiother preheat or start. Pulled out the MDI box and touched the MOSfet. Not warm at all. Still measured as normal. So I put it all together one more time. All seemed ok still. But when I hit the start button (just to check if the starter solenoid kicked in) it just klicked. Not the solenoid, but something electronic, like a fuse or something. I smelled the MDI box yet again, but neither strange smell or hot components. Nothing visually abnormal either. Checked all the fuses I could find, all of them seemed ok. Tried one more time to put it together, but the display was dead. No life at all.
    So what do I do now? Omit the MDI box and rely on old time simple relays, or buy a new MDI?

    • Hello Geir Andre,

      Shorting the glow plug rail to the block will cause damage because this supply is not fused anywhere. The IPB011N04L MOSFETs are arranged in pairs in a somewhat surprising back-to-back series configuration, which means that they can also interrupt any current trying to flow back into the battery. A single MOSFET behaves like a forward-biased (i.e. conducting) diode in the presence of a current flowing backwards through it.

      It could appear overly cautious, but Volvo Penta must have found a reason to adopt this design. Anyway, in the event of a short-circuit, the FETs have no other option than blowing like fuses and one in the pair will almost invariably fail before the other. The most immediate failure mode for MOSFETs is going into short-circuit first, so you could end up with one survivor and one open-circuit, or one shorted and one open-circuit. If you replaced the FET interrupting reverse current and the other one was shorted, then connecting the glow plugs would cause uncontrolled current to flow freely through the shorted FET and then backwards through the body diode of the new FET, dropping about 0.6V on the process. This will cause it to dissipate about 6W in heat per glow plug connected (about 10A current per plug on these engines and 0.6V drop over the transistor). This will cook it in very short order. In this case, you should have replaced the pair and everything should have come right.

      MOSFETs can be difficult to test without first removing them from the circuit. A good transistor will read open circuit from the drain (tab) to the source (5 pins linked together) and like a diode from the source to the drain. The gate (leftmost pin) should be isolated from both the source and the drain.

      The best way to remove SMD components is using a hot air soldering station. With a little bit of care, you can achieve the same with a heat gun on a low setting. You want to heat the parts and the board just enough to melt the solder and release the component. You can use aluminium foil to shield other parts of the board.

      Reading about your last attempt, I wonder whether you successfully removed the short from the glow plug rail. Semiconductors can indeed emit a faint “ping” noise when switching a lot of current and the only part of the circuit capable of this is really around the 4 MOSFETs. I would use a heat gun and lift off at least the two MOSFETs switching the preheat (if not all four), then try the unit without them and the starter solenoid and glow plugs disconnected anyway. See if you can get the display back. If not, then further damage has occurred and you might have to consider one of the options discussed in the article above. You can manually switch the preheat and starter solenoid to get the engine running, but it wouldn’t be responsible to operate the engine without any monitoring on oil pressure and water temperature, so you should at least add these two gauges and an alternator charging light if you don’t replace the MDI box.

      Kind regards,


      • Thanks for the great answer. 🙂
        I found the reason why the display didn’t wake up. When we installed the battery, we forgot to tighten the terminals 🙁 When we tightened the terminals, the EVC display worked again. But the EVC beeps constantly. If I remember correctly, it is the system failure symbol.
        Regarding the MOSFets, I ordered two new ones but did replace just one. So if I replace both the new ones, it might work? I’ll try it tomorrow. Crossing fingers and toes 🙂
        Thanks 🙂

        • It would appear that the clicking noise you heard earlier could have been a spark at the loose battery terminal when the starter circuit was closed and that would be good news.

          If you have a failed MOSFET in the pair, the system might well see it and report a system failure. You should not find battery voltage on the 5 pins linked together (source terminals) of the FETs when the battery supply is present and the FETs are supposed to be off. If you find battery voltage there, then the first FET must be shorted.

          If you heat the board, you can just as well remove both transistors for a start and test them properly away from the circuit. You could also try to power up the module without them and see what the display looks like. You might only get an alarm when you try to preheat because it can’t switch the output on.

          Best regards,


  13. Regarding: “One could opt to install an independent parallel engine start circuit by adding two external relays to connect the “PREHEAT” and “START” terminals to the “BATT” terminal at the push of a button. In this case, the preheating relay must be able to handle a current of about 10A per glow plug, so 40A on a 4-cylinder engine.”

    Are the preheating and start outputs of the MDI box just simple relays? I attempted to look up the part numbers “HAC728” without success to confirm. If so, there should be no harm or risk from applying power to those terminals (with harnesses still connected) using external backup relays, correct?

    • Hello Ken,

      Early versions of the module used relays. Later they replaced these with MOSFET transistors in a configuration that fully isolates the terminal posts. In both cases, you can install a parallel control circuit without issues.

      Can you please e-mail me a picture of the top board in your unit and the MDI box model number? I am curious about the HAC728 reference you are mentioning. It doesn’t match either design and I would like to confirm there was not an intermediate circuit with different components maybe.

      Thanks and best regards,


  14. Eric,

    My MDI box failures have all involved the start-stop functionality: un-commanded stops, inability to stop, or inability to start. At all times, the J/1939 bus has continued to function (I have a J/1939 to N2k interface.)

    How hard can it be for Volvo-Penta to take a button press on the panel and operate a relay in the MDI box to activate the stop solenoid or start solenoid, as appropriate? I realize it’s slightly more complicated because there’s some self-test circuitry involved too: for example, disconnecting the stop solenoid raises a periodic alarm.

    I’ll take a photo for you of a failed 23195776 (shipped, incidentally in a box marked 23231607.) I’ll also do a few tests on it just to rule out the possibility that after all these failures the buttons on my panel haven’t worn out.

    • Jeremy,

      Thank you for writing. Remember that the control functions of the MDI box are precisely limited to starting and stopping. It could have transient issues over CANbus like skipped or corrupt messages and they wouldn’t be visible. There have been many “dead” failures with these modules in the past as they seemed to suffer from electrical transients. Your feedback is interesting as it suggests that this would have been addressed by now. At least one relatively recent version was recalled as faulty and known to malfunction with the symptoms you describe.

      I think that the module operates in relatively difficult conditions from an electrical point of view as it is exposed to the high frequency ripple voltage from the alternator (which, by default, feeds into the starter motor connection, not the battery) and spikes from various inductive loads. There is also a fair amount of attached wiring to pick up transients and feed them into the electronics. While the design and construction of the module have improved a little over the years, they are clearly not “heavy duty industrial” when it comes to the interface between the electronics and the outside world.
      We also tend to focus on the physical module itself and the electronics, but some versions could just as well have experienced firmware problems as such embedded code is always very closely tied to the electronics.

      When you open your 23195776 module, see if you can separate the PCBs if you get the opportunity and also take a picture of the lower one with the processor. At some stage, once I have a little more material available, I will write an article showing and discussing the differences between the models I have received photos for. The design has seen considerable changes over the years.

      Thanks and kind regards,


  15. Really appreciate your article re MDI for the D1/D2 Volvo Penta labeled diesels.
    I have at least 1 more number 3885724. My engines are D1-30B circa 2006/2007. Not sure which but they apparently missed the engine recall either by date or the fact that they were on a European boat which I now own in the US.
    Another puzzle piece. VP sends 23231607 labeled blue parts box with 23195776 labeled part inside. Their explanation per the local VP Certified business… 23231607 is a kit containing 23195776 and a pamphlet of instructions… $800 please (well, they haven’t said please).

    • Hello Martyn,

      Thank you for the additional information, I have added it into the table. As I have never seen a picture of a MDI module labelled 23231607 and everybody reports receiving 23195776 in the box labelled 23231607, it could well be the explanation indeed.

      This would make 23195776 the latest version and, as it has been around for a couple of years now, it may have proven more reliable. Still, I have received photos of the top PCB of 23195776 in failed units, so it may not be the end of this saga.

      Kind regards,


  16. I have a 2010 D2-55F with about 3500 hours and experienced the issues you refer to here.

    Problems started in 2016 with a burnt out fuel solenoid. Was replaced and the replacement burnt out. It was then noticed that the Stop on the LCD was flicking on and off. The MDI was replaced. Within a few weeks we had surge problems caused by the stop solenoid being activated. Also problems with starting. Replaced the MDI again. Also failed, the Volvo dealer gave me their older test unit which I used for a month or so. They got a new revision which has been on for a couple of years without problem. So I probably have the 22594274.

    I noticed there is a 2018 recall notice issued by Volvo for the MDIs. See https://i.imgur.com/YZmExSn.png. Will check with the dealership to see whether I should be upgrading. What I would really like is to have a spare given the horrible reliability.

    • Greg,

      I am aware of the recall. It is quite specific and targets the latest F variant of the engines only, so they were replacing a defective version or even production batch within a version of the MDI module. This can happen. There have been a lot of problems with some versions of the MDI box, but others have also given good service, all have been known to fail and we automatically hear more about the failed ones…


  17. I decided to check the panel on my Volvo D2 and found that the Stop button was not working. The MDI box that I thought had failed (23195776) is in fact working fine. I’d recommend checking the panel buttons in cases of stop/start problems even though the MDI box is the prime suspect.

    • Hi Eric,

      As written in your article: Some modules were also lost due to the addition of ground disconnect relays to the installation on alloy boats because of the unclamped back EMF of the relay coil.

      Now I an owner af an aluminium vessel with an D2-55F with ground connected to engine (2015). Without the MDI its much easier to install a additional ground isolation relay. With my engine and with the MDI I’m struggling how to do this. Please can you advise, how can I isolate the ground/ install an additional relays to minimize contact time with ground/engine (only starting/ glowing).

      Regards, mike

      • Mike,

        For a start, I can tell you what I did about it. I electrically insulated the engine block from the hull by mounting it on thick plastic plates and sleeving the engine mounts bolts. I also replaced the metal Morse cable fork on the gearbox control lever to prevent it from grounding the block at the engine controls. The throttle lever attachment already had insulation. If you don’t do that, you immediately set up a cast iron/aluminium battery cell with sea water as electrolyte, whether the ground is connected or not. Next, I used a plastic ball valve on the seawater intake, so it is not electrically conductive when shut. I also have a 2-pole battery switch to the engine and I turn this off when the engine is not running: it breaks both ground and positive supply. The only anode I have is on the propeller shaft to protect the propeller. I designed everything for zero corrosion and achieved zero corrosion.

        Now, unless Volvo changed the design of the electrical system on newer engines, you can’t operate the MDI box without a grounded block because there is at least one single wire sensor (coolant temperature switch) that relies on a negative block to function, so you can only disconnect the block when the MDI “ignition” power is off.
        If you do fit a ground disconnect relay, it is critical that there is a free-wheeling diode in parallel with the coil to short out the negative spike when you turn it off. I would also want to disconnect the alternator B- post from the block and run a new cable to the battery negative instead so you can’t lose that negative with the engine running. It could damage the alternator.

        The control for the relay would have to come from the MDI power wire on the Multilink cable (but beware of the load increase), unless the whole MDI system was able to operate without reference to a negative block. If this was the case, then you would want to operate the relay using two “OR”-ing diodes from the preheat and start posts of the MDI box.

        As far as I am concerned, a 2-pole battery switch is simpler and better. Disconnecting the engine ground stops grounding the hull through the block, but it doesn’t actually lead to a good outcome anyway if the hull and engine are electrically connected.

        Kind regards,


        • Hi Eric,

          Many thanks for your reply. In the meantime I have been in contact with Volvo Penta France. They do the installation/conversion for Aluminium Ovni boats. I received the electric drawings and part list to modify the engine with additional relais. MDI is not grounded during operation. There is only ground contact during start and preheat. Please drop me an email to share the information. Appreciate your feedback.

          Regards, Mike

          • Hello Mike,

            Then it will require an isolated water temperature sensor.

            It still doesn’t resolve the galvanic corrosion cell problem if the engine block is electrically connected to the hull, but from Volvo’s point of view, your hull acts as a big aluminium anode protecting their engine, so it won’t worry them.

            Kind regards,


  18. Eric,
    Thank you for the informative article on the Volvo MDI. Wiring information is incredibly difficult to find.
    I have a D2-55F with OEM 115A alternator. Now upgrading to an alternator with external regulator. I’m getting an alarm at the EVC panel that I suspect is from incorrect interconnection between the new alternator/regulator the MDI. I’ve disconnected the yellow S wire as I can’t find its purpose for the new regulator. Would this generate the alarm?
    Would you know the purpose of each wire between the MDI and the OEM alternator? According to the OEM Alternator schematics, they are labeled D, S, and W. B+ and B- are self-explanatory.

    • Heins,

      You are downgrading your alternator and it is an immensely stupid thing to do. This was the driver for developing the VRC-200 controller, it just makes the excellent existing alternator fully programmable.

      “S” is the alternator voltage sensing input and if you run a wire from there directly to the battery positive, charging performance will probably increase enormously. Connect “S” to a VRC-200 controller instead and then you can configure any charge profile you want.

      “D” powers the internal regulator. The MDI box applies power to it initially through a small black wire to kickstart the alternator after cranking and then it is monitored for voltage. If that wire doesn’t have power when the engine is running and the battery voltage is below a threshold, the EVC is going to alarm on alternator failure.
      Bare alternators sold without regulator have no D terminal. If you connect the black wire somewhere else (like B+) to try to get rid of the alarm, you will need to check that this doesn’t drain the battery when the engine is off and the MDI box could then complain that D has power before the engine starts, when it shouldn’t.

      “W” is an AC output to drive a tachometer, you don’t need to worry about it.

      Kind regards,


  19. Eric,
    Thank you for the fantastic work you do.
    I have an odd start problem with my D2-40B, serial 5102001879. After 11 years w/o problems it began this summer to fail to start when finishing sailing w sails. When pressing the start button the power simply cuts. A few time it starts after power up the power button on the panel, but else I have to switch the main engine breaker downstairs of and on. Hereafter it starts w/o problem.
    When it fails to start there is no power from MDI to the starter relay (I put a lamp on). Other panel functions like engine stop, engine alarms, power up etc also works fine. (The neutral switch is apparently not active, I can start in gear, but has always been so).
    The MDI Volvo part number is 3885724, i.e. one of the old ones.
    I can’t figure out what it mean that I have to cut the engine main to reset the system. My best guess is something to do with the MDI box. Have you any suggestions?
    Best regards
    Henrik Holten Møller

    • Henrik,

      Thank you for your message. My guess, considering the age of your MDI box, would be that the electrolytic capacitors on the top PCB have dried out. They are no longer able to act as a buffer during the transients caused by the chain of events leading to engaging the starter solenoid and it causes the CPU to crash/lock up at times. When this happens, you have to turn the power off completely to reset it.

      Your MDI box is the next version after mine. It should not be very different inside than the one I show on the photos in the article, with two 220uF/63V electrolytic capacitors. I would open the MDI box, separate the top PCB and replace the capacitors with new ones. It is an easy thing to do with just a soldering iron. Use good quality capacitors with a life rated at 105degC. Please send some photos if you get a chance, this is a model number I have never seen open.

      Kind regards,


    • I had the same problem. I traced it a bad battery cutoff switch. I changed out the switch and no problems now.

  20. Hi Eric,
    How do I separate the 12 pin connection between the boards in the capacitor end? Pull apart or de-solder? They seem very tight and I’m afraid to damage connection and boards.
    Rgds Henrik

  21. Enjoyed reading your analysis. I have the D2-55F that installed in a Slocum 43 (circa 2016). From the start I had issue with EVI guages as the voltage meter was constantly out… although the NMEA 2000 read out on the Garmin MFD read correctly. ….The dealers solution was to replace the MDI ! .. clearly that didn’t fix the issue. VP has been unwilling or unable to provide a correctly scaled Voltage meter. The following year the replaced MDI simply failed to light up (and the engine wouldn’t start) Replacing that one did fix the problem until June this year… and another one was sent fixing the problem … until last week, after 6 weeks of not being on the boat (hip replaced) . I engaged the connection switch and the engines hours immediately showed and when I hit the ON button (not the START button) the engine started immediately! I let the engine run until the engine reached engine temperature…. and I hit the STOP button until the engine stopped…I removed my finger and the engine started again “on it’s own”….. This was bazzar. So I then held the the STOP for a full 30 seconds… It remained off. The engine’s hour meter remains “on”. The ON /OFF button has no affect on the hour meter and the engine will not start! I would disconnect the battery but I had the same problem two weeks ago. I literally have no faith in the Volvo Penta System… but until I source all the conventional gauges and parts necessary to replace it outright …. I have to work around this… it is clearly an intermittent problem… This will be a fourth MDI …. any input would be greatly appreciated!

    • Thomas,

      I would look at the small control panel with the On/Off, Start and Stop buttons. Any dampness in there could cause control issues. You could remove it and try drying it for a start.
      Next, I would ensure that the connection and cabling to the battery are very good throughout. Repeated MDI failures usually have an external root cause, i.e. on board. The module itself is not that unreliable, but electronics are sensitive to electrical transients.

      All the best,


      • The controller is “potted” sealed in the back and there is no feasible entrance from the front. I don’t see how it could wet or how to “dry” it if it is wet. I am burnishing all connections and torqueing the bolts between the battery and the engine and to the remaining 2/0 AWG and smaller cables to the MDI.

        I disconnected the battery from the system and tried a restart… now the system when started will start ticking and Volvo Penta comes on the Tachometer and then immediately stops. The engine will not start… the ticking remains for about 15 seconds ….then it’s dead. It will not react again unless the battery is again disconnected…. Then the same sequence until it dies again. This MDI had 41.8 hours on it.

        The Volvo Penta D2-55 is actually the successor to the Perkins 4-108… It is a Perkins 4-134 if you will. Perkins secures the CE certification before it is relabeled a Volvo engine. The engine is actually a sturdy beast.

        Having thought about it, even if this can be fixed… The safety of my vessel and my family cannot be left to chance that a voltage transient could eliminate auxiliary power at the wrong time. Think sensitivity to lightning. A purely electrical alternative, while not perfect, has been proven to be a far more reliable and seviceable option. I am really left with no other choice. I am currently waiting for the “Volvo Service Tech” to find a “hole” in his schedule to see fit to install the “next” box. He has had the box now since Monday. The system has been down for three weeks.

        • Thomas,

          Yes, it is potted around the back, but not sealed quite as well around the buttons (membrane keyboard) and any moisture in there could make some of the buttons read as if they were depressed. I would just warm it up to 50degC for a few hours in an oven and see if it helps. Alternatively, try with another control panel if you can.

          The behaviour you describe is a bit disturbing. I would check what the voltage is doing on the supply to the MDI module for a start, especially while cranking. How low does it get?

          There are simple ways to bypass the module to operate the engine (see in the article above) and you could try that and see if the MDI/EVC system behaves after the engine has started (reboot the MDI by pulling the main power plug after the engine has started if needed). If mine was acting up like that and I couldn’t get to the bottom of it, I would retrofit the engine with analog gauges and senders for all the reasons you describe.

          Best regards,


          • Thank You Eric,

            Thank you for your advice. Your suggestion about the “potted” control panel was one I had considered from the beginning. I am beginning to think that the MDI is not defective. FYI the module is a 23195766

            I have started the engine using a jump start across the start solenoid. The instruments “wake up” and operate per normal and Nemea Gateway allows the the MFD to represent Tach, Voltage, and Temp gauges operate per normal. However the Stop button may or may not work (intermittant) and the engine hours remain until I cut the battery switch connection.

            After tightening all the connections…At the battery and the MDI the battery shows 12.8 volts max and drops to minimum of 10.8 or 11 volts at the battery at start… and min of 9.7 at the engine buss, and 9.4 volts at the MDI batt pin. There is about 12 ft of 2/0 AWG cable between battery and engine.

  22. Hi Eric,
    can you give me any information about the auxiliary connection?
    Can I use it to drive an external relay?
    Thank you

  23. My brand new D2-50 has failed at 5 hours due to a faulty MDI. The unit will be replaced under warrantee but I am very uncomfortable having a potentially unreliable weak link in my engine system. I do a lot of my sailing in remote places and this is not seaworthy enough for my liking…

    I want to install an emergency bypass start / stop switch on the side of the engine box, capable of being used for an extended period, not just as a one-off to get me back to the marina!
    I understand how i can introduce a straightforward starter switch:- one for the starter motor, one for the glow plugs. However, I am not sure about the stop solenoid. Does this require power to open, or power to close the solenoid, and which wire do I link into? Do I have to do anything to make the alternator work too?
    I would be really grateful for any advice on wiring up a robust emergency bypass system

    • Hello Simon,

      It may have truly “failed”, or it may have been damaged. One of the main destruction pathways for the MDI box is bad connections between the engine and the starting battery. I would have a very serious look into this, including the isolation switch, before restarting the engine with a new MDI box.

      The injection pump has a stop lever on it. Use this, don’t interfere with the electric stop solenoid.

      Kind regards,


      • Thanks, I will check this out. Presumable then the stop solenoid will not prevent the engine from starting even if the MDI is dead?

        • Simon,

          On a conventional marine diesel engine, the stop solenoid is normally energised to stop, because this is the fail-safe pathway.
          Volvo engines using the MDI module are mechanically injected and they follow this principle. Once started, they will keep running even without any electrical power.

          Kind regards,


  24. Many thanks for all your help. It is extremely kind of you..

  25. Checking the battery switch my attention turned to the VSR. It is currently connected conventionally, with charge going first into the start battery. I want to change it round so that charge goes into the much bigger house battery, which involves a new battery lead from alternator to house battery and connecting the start battery directly to the MDI. Will this affect the operation of the MDI and alternator? ie: must the alternator need to be connected to the MDI positive terminal for everything to work properly?

    • Simon,

      Connecting the alternator output to the house bank is always preferable, but do yourself a favour and also move the yellow voltage sensing wire to measure the battery being charged. A battery isolator is a better choice than a VSR by the way.

      Kind regards,


  26. Thanks, I fitted my emergency bypass switches yesterday, with the dead MDI unit still in place. They work just fine and they have also made the dead MDI unit come back to life! I started and stopped the engine many times with the switches and with the MDI, which now seems to be working normally.
    The code on my MDI unit is P22458510 if that is any interest to you…

    • Hello Simon,

      Then there might not have been much wrong with the MDI box. The only difference is that you have touched the wiring.
      The part number you are quoting seems rather unusual.

      Thanks and regards,


  27. Operating a fleet of yachts, we have had plenty of experience with the MDI units over the last 15 years and we can categorically say that 90% of failures can be attributed to the Volvo start panels and have little to do with engine heat and vibration, Volvo are trying to save some cash with this story – the start panels are not waterproof so the contactors engage periodically which hold the relays inside the MDI on and burn them out. Often it’s the heater plug circuit which causes the damage because the top right button is the power on/heater circuit on button it gets wet first. We have tested this extensively. We moved some of our 60 EVC control panels inside and the only subsequent failures are on the boats with original start panels exposed to the elements. Best advice: Mount the start panel inside or as we have done, manufacture your own aftermarket start panel (only difficult bit is putting a resistor inline to drop the voltage) – we also included a light so you know when the panel is actually on and off rather than relying on the tacho display (also prone to failure)/fuel gauges. We replaced all the MDI’s under warranty but the boats with exposed star panels still replicate the same issue very quickly.

    • Chris,

      Many thanks for taking the time to write, yours is an interesting perspective for sure. The early MDI boxes (like mine) DID break as a result of heat and vibrations, I have photos illustrating it that I will publish one of these days. It is not a “Volvo story” and it wouldn’t help them in any case. In all the later versions of the module, Volvo revised the design to use all surface-mounted parts and also replaced the mechanical relays with solid-state switches. These won’t burn out even if left on and the newer design is more resilient to vibrations. Heat is still an issue on the long term because of the continued use of electrolytic capacitors.

      I was aware that MDI problems sometimes originated from the little EVC control panels. It is very interesting to learn that it can be so systematic. Problems with the control panels often materialise as malfunctions, stoppages, inability to start etc. I have never been exposed to these issues because I installed my EVC panel inside from the beginning as a matter of principle.
      Building replacement control panels makes a lot of sense, but I have never had the opportunity to reverse engineer their design or investigate the signals on the 4-core cable.

      Kind regards,


      • Hi,

        > but I have never had the opportunity to reverse engineer their design or investigate the signals on the 4-core cable.

        These are documented in the D2-40F workshop manual for the electrical system (google will find it) such that it is. Documented, in the sense that you can work out what they do from the tests. One of the cables transports switch information from the control panel to the MDI, including things like the neutral position micro switch. The other 2x CAN busses (1 per engine, joined for 1) with J1939 messages (not NMEA2000) on it. A full list of messages is detailed in the Yacht devices YDEG-04 user manual including the Volvo Penta custom messages (status values and trouble codes). Since most engines with a MDI are not exactly sensored up in the way that a full ECU engine would be, to be honest, I am not certain how interesting the J1939 messages are over one of the generic engine -> NMEA2000 converters which are widely available.

        I have a D2-40F (2017) with a MDI replaced under recall, and suspect if it fails I will do as you say, replace the switches with a custom panel and use a engine->NMEA2000 to get data onto the sailing instruments/MFD (currently using https://github.com/ieb/EngineMonitor, based on a ESP32, which seems to work ok to a Raymarine e7 MFD), or use a generic Tachometer from the W+ terminal.

        I am very tempted to move the MDI away from the heat and vibration.

        Best Regards

        • Hello Ian,

          We don’t appear to be talking about the same cable here. What you are referring to is the Multilink cable from the MDI box to the tachometer, which contains cores for power and twisted pairs for the engine CANbus. The cable to the small control panel with the buttons is something else. While I have indeed found some documentation about it… it shows a 6-core connection to the MDI box whereas mine is on a 4-pin plug. Have they changed the interface on newer MDI modules, making them incompatible with earlier control panels? Apparently so! Replacing the MDI box on my D2-40B would then prompt also replacing the control panel.

          Thanks and best regards,


  28. Hi,
    I am talking about both cables.
    I think the information you want is on page 33 and 34 of the D2-40 workshop electrical manual which you can download from https://www.plaisance-pratique.com/IMG/pdf/MID.pdf Page 33 has a diagram of the plug. Page 34 has the test procedure for each wire.

    If there is another cable other than the button and can bus cable, sorry of the noise.

    Hope that helps.
    Best Regards

    • Ian,

      Yes, I had found the same document and it does detail the pinout of both cables indeed and it is very useful. I need to have a look at the body of my article again with this information.

      My control panel cable has 4 cores only however and I have also found a 2013 version of the workshop manual, but none showed a 4-core cable.

      Thanks and kind regards,


  29. hi Eric,
    i had a similar problem.
    after 5h running, suddenly the motor stopped (in front of the lock!). the power supply was ok upto the black box. it seemed not to transmit voltage to the control panel. i had to shortcut the start circuit to drive further. the next day the control panel had voltage again (we didn’t do nothing!). now WE THINK everything is normal again. but i still have to check that the alternator is loading the batteries.
    my engine is brandnew. installed november 2020/ comissioned april 2021!
    i reported it to the installer of the engine. he will ask volvo penta about this problem. still lots of questions wil stay.
    if i will continue with this MDI module, will some parts be damaged and cause problems on long terms?
    if i read it correctly, it is not necessary to have the MDI module? only for start en read the engine functions?
    kindest regards

    • Sven,

      Because your engine is brand-new and under warranty and the Volvo EVC system is normally very reliable, my advice would be NOT to start modifying anything. Check that all the electrical connections are tight, because bad contact/transients can cause the electronics of the module to reset, lock up etc. The fact that the engine stopped is unusual because this requires an action from the MDI module. Sometimes this is caused by a faulty control panel with a shorting stop button that sends the command to the MDI module. Unplug the control panel from the MDI module and reconnect it, making sure the plug is fully inserted and locked. Be aware that your engine could stop (an engine can always stop unexpectedly after all) and see if it happens again, because it could be difficult to get the dealer to do something based on a single isolated event.

      When the MDI module fails, you lose the engine gauges and the ability to preheat, start and stop. If the engine is running at the time, it normally keeps running. The engine itself is purely mechanical and doesn’t require any electrical supply to function.

      Kind regards,


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