Replace Your Automatic Transmission With A Bunch Of Relays

A “Check Engine” light on your dashboard could mean anything from a loose gas cap to a wallet-destroying repair in the offing. For [Dean Segovis], his CEL was indicating a fairly serious condition: a missing transmission. So naturally, he built this electronic transmission emulator to solve the problem.

Some explanation may be necessary here. [Dean]’s missing transmission was the result of neither theft nor accident. Rather, he replaced the failed automatic transmission on his 2003 Volkswagen EuroVan with a manual transmission. Trouble is, that left the car’s computer convinced that the many solenoids and sensors on the original transmission weren’t working, leaving him with a perfectly serviceable vehicle but an inspection-failing light on the dash.

To convince the transmission control module that a working automatic was still installed and clear the fourteen-odd diagnostic codes, [Dean] put together a block of eight common automotive relays. The relay coils approximate the resistance of the original transmission’s actuators, which convinces the TCU that everything is hunky dory. There were also a couple of speed sensors in the transmission, which he spoofed with some resistors, as well as the multi-function switch, which detects the shift lever position. All told, the emulator convinces the TCU that there’s an automatic transmission installed, which is enough for it to give the all-clear and turn off the Check Engine light on the dash.

We love hacks like this, and hats off to [Dean] for sharing it with the VW community. Apparently the issue with the EuroVan automatic transmissions is common enough that a cottage industry has developed to replace them with manuals. It’s not the only questionable aspect of VW engineering, of course, but this could help quite a few people out of a sticky situation.

80 thoughts on “Replace Your Automatic Transmission With A Bunch Of Relays

    1. Well that is interesting, when I did the swap in mine years ago, I went to the dealership and had them recode the transmission from a 3 designator for auto; to a 1 designator which is manual. Afterwards I drove at 500 miles and never had a check engine light, never had those codes pop up again.

        1. Waste of time, fire up VCDS (even cheap Chinese clone would work). Go to abs module recorded that, , then engine, transmission coding, that’s all, it’s probably much simpler than wiring everything again then still you don’t have for example speed sensor if it not codded correctly, even better you can fin all instructions on rossTech wiki and forums

  1. Good for you, Dean! I had a 2001 Eurovan, and while I loved the van, I hated the constant trouble and expense with the automatic transmission. I would have replaced it with a manual if I could have found one (only automatics were imported into the US). Instead, I sold it after the 3rd multi-thousand-dollar repair bill.

      1. The idle controller is a carefully tuned set of PID controllers in the engine control module. The different inertia of the various flywheel and gearbox combinations requires significantly different parameters. (Tuning these controllers was my actual job until last year). The only way you will get the idle controller to be happy would be to get the manual gearbox software variant flashed to the ECM. Spoofing the presence of the auto box won’t particularly help here, the problem is physical.

  2. Isn’t it possible to just remove the TCU and flash the ECM with the manual calibration?
    This might need to be done by the dealer, but ought to fix the problem properly. (eg. gear ratio detection will be correct so the idle controller etc will all work properly)

    There might be remaining issues with the BCM configuration, but then I imagine that this hack isn’t a 100% fix either.

    (Today I have mainly been working on the 2024 model…..)

    1. Yep as another commenter posted this is possible using vcds (an aftermarket vw diagnostic tool) you edit the “long coding” in all the pertinent modules to tell it that it’s a manual not an auto and good to go.

      1. It’s a bit more than changing the options, in my (limited) experience. The manufacturer I work for ships completely different calibrations for auto and manual. The PCM firmware consists of the software (Strategy) and the data (Calibration). The latter is all the maps, curves and values that are inputs to the software. (several thousand maps, tens of thousands of individual variables). Quite a lot needs to change in areas such as PID gains and torque maps to deal with the different transmissions. (It is even possible that with the right setup the engine will be allowed to make more torque with a manual configuration)

        1. It is possible, at least for most VWs. Perhaps theres something specific for your situation but it works with other similar age VW models so I don’t have any reason to believe thats the case. Still this is having some spillover to VWs in general so a more general reply seems fitting.

          Above is one of many walkthroughs on how to do it with VCDS. The problem here may be that you’re trying to talk to the TCU instead of just circumventing it since its not necessary anymore. Thats just a guess on my part though.

          1. Im not a master tech or anything.. but have seen this done on multiple gassers in my 20+ years of working on Beetles. Then again the official techs often said fixes were impossible at the same time the community was doing that very same thing on the regular.

        2. This is exactly what many more need to do with these every new unable to repair vehicles we have these days. Need more ingenuity like yours for all types of code. Especially when moding our vehicles. I like what you done it is classic.

      2. I think did single use use cases like this, ObdEleven would have been cheaper option. Or even visiting the stealership is one option but I think whole ObdEleven pro pack would have been cheaper than that.

      1. What’s the roadblock to this? Is it that there is no factory manual gearbox option? Or that the PCM is different between the two variants (eg, integrated ECM / TCM or some other incompatibility.)
        Or is it just that VW (or their systems) simply won’t allow a manual software flash to a vehicle registered as an auto?
        What happens if you “just” fit a manual ECM to the vehicle? (I would anticipate a lot of unhappiness on the parts of various modules, a factory re-marriage process is likely to be needed)

        You hack is cunning, and cheap, and seems to be effective. I am just interested in what prevents the modification being done in a less hacky way. Which, on balance, is a bit off-target for here isn’t it?

        Be as technical as you want in your answer, my day job currently involves control module integration in the upcoming model of the VW van (not going to be made by VW, so I can’t help with yours)

    1. Depending on where one lives, this modified hardware might be flagged as illegal. Now whether or not inspectors catch it is another question. In the US, probably as long as the catalytic converter is still there, you’re good to go. On the other hand some of our European friends have to endure periodic grueling mechanical inspections and this trick probably wouldn’t make the cut.

      1. Taking out the lamp doesn’t make sense but the hardware trick would make the cut anywhere in the world, they wouldn’t even have a clue what they’re looking at.
        Probably it wouldn’t pass cause it’s listed as auto but it’s manual. But no tech inspector would notice the tech hack if you don’t leave it out as a complete hack job.

      2. In most states, so long as you aren’t violating any state or federal safety/environmental laws, any modification is fine. It’s basically a “so long as there isn’t a law already covering it” situation then you are good to go. Blanket statement laws like “you may not modify a car in a way the manufacturer deems unsafe” are generally considered unconstitutional and rarely make it out of federal court. There would have to be a specific “a CEL may not be removed/replaced with a bypass” law. Or a “you may not swap transmissions from one type to another” law. I could see a CEL law, but a transmission swapping law wouldn’t make any sense. Laws in the US generally have to be fairly specific to hold up in court.

        I get what you mean by the only needing a catalytic converter though, seems like some states only care that your car isn’t polluting the environment, safety be damned so long as mostly nobody dies. I’ve had cars with holes in that a large house cat could sail through pass inspection, but had cars in perfect condition fail completely because of a crap O2 sensor on the exhaust. Doesn’t make any sense.

        1. In NJ, 1995/older gas cars under 8k lbs, 2007/older for gas vehicles 8k – 14k lbs and gas vehicles 2013/older which are over 14,000lbs are all exempt from emissions, safety, and inspection altogether. Pre-2016 when this was legislated, the Police –or as the homies call them, “the poe poe, the fuzz, 5-0” and the least popular (😂) “hey my rides here,” were bringing home the bag for their respective county or precinct or state. They’d consistently harrass all of the older cars with outdated inspection who wouldn’t pass the emissions test if they were fresh off the line new and came in a time portal. It was a total sh*tshow and it went on for my entire teens and 20s. Useless legislators finally caught onto their little grift as result of conflicting laws and passed changes in 2016.
          Can imagine what it was like before catalytic converters were invented. I imagine the air quality was similar to present day China. Take a motorcycle ride in China– you’re covered in a layer of fine dust particles as if you’d been working in a shop when you’re done.

    2. Given VW’s past approach to passing regulatory tests the obvious solution would be to spoof the OBD port when an inspection is detected. Inspection detection could be a hidden switch the driver switches before dropping off the car. Imagine a whole line of VW branded gray/black market OBD interposer circuits activated by a remote switch to report a clean bill of health.

  3. It is comforting to read that as aging automotive sensors/components fail, and replacements become harder to source, hackers will be able to keep their automobiles 🚘 on the roads and not sending them to the junk yard.

    1. I was reading the shop manual for my 2001 Honda Insight. Supposedly the engine control unit is still able to operate the engine in limp-home mode even if the CPU fails. Now the odds of the CPU failing without other absolutely necessary hardware in the ECU being damaged simultaneously, my guess, are pretty long shot. If would be interesting to know which sensor inputs are critical (crank angle, for example) to keep operating, albeit operating poorly.

      1. 2001 is of an age where the spark may be triggered by a standalone module that takes a spark advance offset input from an ECU but if it doesn’t have that offset it still produces a spark at a safe default. That’s how the Ford EDIS module I stuck in my project car works: the module is hooked to a crank angle sensor and send out RPM data to the ECU, but can work standalone if the ECU isn’t doing anything. It was from a late 90’s car.

        1. I think there is a good point here regarding resistors, since it’s 12v DC the relays are simply resistive anyway, dissipating the same power as the equivalent resistor (if you measure the relay with a ohmmeter). This is usually in the range of 1-3W. Not that hard to dissipate from a resistor. Chances are a higher value resistor would have worked too, like these $0.5

  4. Finally! A “right-to-repair” article—not about the politics, but about how to wrangle the “chewing gum and bailing wire” of the 21st century.
    Dear HaD Editors: please bring us more—not so much as to turn this site into Car Talk, but to showcase the clever Hackaday sprit in the automotive realm.
    Some of you may know that VW has fostered a long tradition among “atom hackers” of DIY repair, from the very beginnings of their first “quasi open-source, almost motorcycle with a car body around it.”

  5. I’m gonna be entirely honest, I did this to the first car I ever owned and with a much simpler solution. Similar scenario, I had replaced my auto trans with a manual trans and even upgraded my 4cyl into a 6cylinder. Normally I would have sourced an engine control module and harness for a matching vehicle but none could be found so I was stuck with a transmission control module that was looking for a transmission and an ecm that was verifying it’s existence. What I did was fool the speed sensor for the torque converter by using the crank signal, and then simply used an automotive series of 194 bulbs to simulate the loads of a solenoid. A lot of time with actuators you only need to be able to handle the load, not necessarily match the exact resistance of the load especially when the solenoid is internally grounded through the trans case/valve body. These bulbs can take the full load of battery voltage any time and it also kind of looked cool if you placed it where you could see it while driving. Pressure control solenoids are duty cycled so that flickered based on input speed, while the others were on/off based on which gear the car thought it was in. This helped my bypass OBD emissions on inspection and allowed everything to function with no check engine light. Plus if a bulb went it was easy to stop in to any auto store and get a bulb quick and change it under the hood, and I can guarantee that a bulb probably held up better long term than a relay and costs much less to achieve the same task.

  6. Questionable VW engineering: The bottom bolt hole, for the bolt holding the compressor on a 2008 VW Jetta opens into the compressor tensioner slot. If you accidentally put the top bolt into the bottom hole it locks the tensioner I’m place. The bottom bolt is about 1/2 mm shorter to stop contact.

  7. This is a really clever hack that demonstrates how a little bit of creativity and knowledge can solve a problem that might otherwise be quite frustrating and costly to fix. It’s interesting to see how [Dean] was able to use a block of automotive relays and some resistors to create an electronic transmission emulator that convinced the transmission control module that a working automatic transmission was installed, even though it had actually been replaced with a manual transmission.

    1. That is what the gear shift lever on the manual transmission he installed does. His relay board just convinces the car that the automatic tranmission is still there so it does not light the check engine light and cause a failed inspection

  8. My car uses the same ECU as the Eurovan and I bet I’d be able to disable the CEL and associated P-Codes for the automatic transmission. I’ve already had to make some modifications for other things.

  9. Does this apply to dodge mini vans because I’m left with a 2013 dode dam cv after a transmission replacement(used) this led to the computer being replaced a ignition module being replaced and while at the mechanics code p0882 always came up,after about 6 months in the shop they told me
    It was the tipm and it was not available any help would be great

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