ECU Rebuilders

[VAEV1993]

I changed the title of this thread, because out of the issue I had below, it seems clear that an ECU we swapped in last Fall for my failed MAP sensor unit, is wrong enough to be causing my issues.

I am searching to replace my original with the correct part number, (023 906 022J), but in the mean time, I wanted to reach out and see if anyone has had good success with any particular ECU rebuilder?

Ecu part number in place now ends with and A.

There seem to be a lot of rebuilders out there, but a few of the initial phone calls I have made seem a little iffy, and a few of the reviews I have read are pretty bad. Anyone had any luck?



***Original issue from this thread is below****


Looking for some others with experience with the 00521 CO Potentiometer Fault.

'93 - AAF - A/T

I am having an issue in that the engine will shut off in the following instances:

- Reverse > Throttle > Brake - So basically giving it some gas when backing up - when I brake to stop, the engine speed will drop low enough below idle and then the engine will shut down.

- Similarly - this will happen then when in drive from a stop. If I give throttle to move forward a short distance and brake quickly - the same will occur.

- In normal road driving things seem to operate fine. Runs well, starts well, coming to a stop engine speed comes down to idle just fine. Idle is stable at about 775 rpm. But these instances where I need to do short backup and/or pull forward maneuvers I lose RPM and the engine...(Pulling out of driveway, into garage, maneuvering at a campsite...these situations)

I used my OBDEleven tool with the OBD1 adapter and was able to connect and read that I had an active code for:

00521 - CO Potentiometer Fault - Open Circuit/Short to B+

I've been down similar roads with engine stall, etc. and last fall resolved that issue finding that the ECU had a MAP sensor failure. I would expect, if I had another bad MAP sensor that I would see a code for that...Or at least...I would hope?

From my searching and reading it seems the CO Potentiometer was installed in vehicles built up to January '93, and after that a Close Throttle Switch was used. My van was built IN January of '93, and from what I see - I do not have the CO Potentiometer. Would someone have any idea why I am seeing this code then?

There were no other active codes, all of my other ignition sensors/senders are all seemingly in good working order, or fairly new (Coil, Hall sensor/Dist., IAT, IAC..). Admittedly have not had time to test any in actuality, but just now concentrating on this code that I see...and starting there.

Any thoughts would be appreciated. Hoping to find time to do some more diagnoses...
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1993 Weekender - Hula
2002 Golf TDI
2017 Golf Alltrack

[VAEV1993]

Bumping this up. I changed the title and updated. Looking for input on ecu rebuilders.
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1993 Weekender - Hula
2002 Golf TDI
2017 Golf Alltrack

[bunkbed]

Would not recommend "neatautocomputers" on eBay. I sent them my ECU after my van refused to run, thinking it had a MAP sensor failure. They returned my ECU shined up and looking nice, but I still had a dead van. Swapping in a good used ECU fixed my problem. In my opinion, a rebuilt ECU should have done the same trick.

[IdeaNerd]

We had an ECU rebuilt in 2017 by a firm up north that our mechanic deals with. Worked well for us. I'll see if I can get the contact info for you and will update with it. Hopefully tomorrow.

[IdeaNerd]

The firm that rebuilt ours was VAR Parts.
varpartsma.com or varpartsma on eBay
It's worked well for us.

FWIW, our mechanic has also used Neat Auto Computers quite a bit for MBZ and BMW ECUs, with good results. That sounds like a very different experience than @bunkbed had, but sharing it here anyway as another data point on them.
neatcomputers.net or neatautocomputers on eBay

Hopefully helpful information. Do let us all know how the situation works out for you.

[VAEV1993]

Thanks much friends. I will keep you posted on how things turn out.
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1993 Weekender - Hula
2002 Golf TDI
2017 Golf Alltrack

[mfaas]

Hi all,

Can't believe I found this thread. I'm experiencing the exact same issues, only your explanation is far more articulate.

My 93 MV AAF MT stalls while under the same conditions and I'm also pulling 00521 CO Potentiometer, which I was under the impression was the air intake temperature sensor. I've replaced that twice and still receive this error and issue has not improved. Also replaced O2 sensor. MPG is also down.

My AAF has the throttle closed sensor as well.

Did you resolve your issue? Was it the MAF? Did it require a new or rebuilt ECU?

Thanks, looking forward to learning from your experience.

Mike

[VAEV1993]

Gosh - yeah sorry I never followed up here on this. I forgot I even posted this to be honest.

The short summary of my situation as that we were having the typical issues with stall out and odd running, and issues with hot start. After all of the other routes of diagnosis, it was found to be the MAP sensor in the ECU. Our shop had a parts van and swapped over the ECU and we were on our way.

Then we came to these problems as described in my initial post and the confusion based on the one code I was getting.

The result was...

The replacement ECU was the wrong revision. I think we had an ECU A when we needed a J unit.

I was able to track down an ECU with the matching part number and revision letter from a junk yard and we were back running again and the CO Potentiometer code was gone. Because the correct ECU was not looking for something we did not have.

Still...things were not perfect, and the replacement ECU had a failing MAP sensor also...(LONG SIGH).

So...then I proceeded to go back to our original ECU, order the MAP sensor from the interwebs, and swap it out on my own. It was not difficult, and we have been running very strong ever since. I made some notes on the swap here in the thread on the van itself.

https://www.thesamba.com/vw/forum/viewtopic.php?t=683873&postorder=desc

Along with what others described in this thread I also spoke to Slavic of TDI Conversions. He offered to rebuild the ECU as well. In the end, I was able to tackle it myself. Though, it there were other problems with the ECU, besides just the MAP sensor - I would probably have looked for some help.

If you have narrowed it down to the MAP sensor for sure, it is not a difficult task if you have a little soldering experience. Probably not bad if you don't have any either. I've seen a good number of posts in the Eurovan Facebook groups of others doing this too.

All the best.
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1993 Weekender - Hula
2002 Golf TDI
2017 Golf Alltrack

[mfaas]

Thanks for the informative reply. I suspect I may not have the correct ECU, since I do not appear to have a CO Pot but also pull that code. Additionally, when I purchased the van, it came with an additional ECU.

Thanks again!

[VAEV1993]

I have been trying to compile a list of the part number and how they should relate to your specific van and build date, etc. I can't say this is all certain, but it might help you refer to what you need if you do not still have your original.

For comparison, the MT GLS van I have for parts has an H ECU.

Obviously it is not complete....
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1993 Weekender - Hula
2002 Golf TDI
2017 Golf Alltrack