# no power to ecu? help please!



## pedrow (Jul 18, 2009)

I have a 2000 Audi A6 (that had an ART 4.2 engine). I replaced the engine with a 4.2 out of a 2002 S6. There is a difference in a few of the wires to the ecu, but I believe (since I have gone through that several times to make sure it is correct) that is all fine.

The problem I am having is that I cannot see the ECU with VCDS on the car. I can get to it on the bench. Also, the car will not start. No fuel pump kicking in; nothing.

It seems that I do not have power to the ECU, but I can't figure out why.

I hope someone can shed some light on this. Basically, the ECU relay is not energizing. On pin 23, I do not get ground (which comes from the ECU to energize that relay).

Also, on the fuel pump relay, the ground signal from the ecu is not there.

I had the immobilizer defeated. So, my thought is that at this point it is strictly plug and play.

Any thoughts that might help me get on the right track? 

Thanks...


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## Eric D (Feb 16, 1999)

Prior to the swap, what this an issue with connection to the diagnostic port?
Did the prior engine run?

If the vehicle has an aftermarket radio with plug and play adapter, verify on the black 8 pin connector that pins 1 and 3 "blue wire" are not jumper-ed together.
If so can you cut the wire off, this is a carry over from the early 80s cars which had no K-line diagnostic.

If the radio is original, then turn your attention to the ABS module, disconnect the big electrical plug and set aside. Now attempt to communicate with the ecu via the diagnostic port.
If it works the issue is a bad ABS module. I discovered the simple fix back in '05, a metal wire under the black plastic cover acts like a fuse and the module looses power.
You can search the web for the a diy. I never posted my results because of a litigious society, since this info is now in the public domain I'm off the hook for any liability.

Since you seem to have lots of cars parting out, I hope you have some basic tools for troubleshooting electrical issues.
Mainly get yourself a Power Probe ECT2000 for easy wire fault finding. I own this inexpensive tool plus break-out boxes for finding wire breaks in a harness.
The Power Probe with wireless transmitter and receiver allows you to find a break or short in a harness and pin point the exact location.
You can't do that with a multi-meter, you have to cut the tape off or sheath, peel it back or remove components in the way to find the issue.
The power probe is a time saving tool and a must have.


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## pedrow (Jul 18, 2009)

Thanks Eric. I will look into that tomorrow. I did unhook pretty much all accessories, like abs controller and radio. I don't think I have a problem with the K-line because I can see the instrument cluster on vcds. The engine set up that I installed in this 2000 car, came from a running 2002, so it should be fine. I appreciate the thoughts. Hopefully, I will be able to find the problem. I will update. Thanks.


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## pedrow (Jul 18, 2009)

Thanks so much. Pin 21 had no power. Once I connected power to it, the vcds recognized the ecu and car started. Thanks Eric.


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## Eric D (Feb 16, 1999)

Thanks for the follow up. I've replied to many posts over the years and many do not reply leaving us wondering what happen.
:beer:


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## pedrow (Jul 18, 2009)

For anyone considering installing an S6 engine/ecu in an earlier A6, make sure S29 is fed according to the diagram. I assumed that S29 was fed properly and did not notice that the white pin near the ECU which is supposed to connect to that fuse, was actually not connected to the fuse, and the coilpacks were getting power from elsewhere. The car started but I was not getting throttle response.


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