Jul 262019
 
Volvo Penta MDI Black Box Overview

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.

Background

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
21120871  
21511215  
21558929 2014
21558939  
22458451  
22458451-P 2017
22594274  
23195776 2018
23231607 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 EVI 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. 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.

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.

Conclusion

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.

  20 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,

    Eric

  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,

    Eric

  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,

      Eric

  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
    Lorenzo

    • 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,

      Eric

  7. Hi Eric,
    Interesting article, thanks!
    I have a 2006
    Volvo Penta D2-55-C
    868971
    5103955405
    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,

      Eric

  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,

      Eric

  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.
    KJ

    • 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,

      Eric

  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,

      Eric

  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.

    Jens

  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,

      Eric

 Leave a Reply

(required)

(required)