A6 4.2 Quattro

Well like the title say's I am having a few issues.

I recently purchased a 00 A6 4.2, it had alot of engine codes. So we began looking over the car, found 2 issue's got rid of 4 codes.

We the other 10 codes are all under fuse 34, for the ecu. This car has 3 fuse's for the ecu.

Well fuse 34 was blown, so we were kinda happy as this would take care of alot of our issue's. We put a new fuse in it, started the car, it was still idleing weird, turned it off, smelled burnt electronics. We started to pull the under dash off, and I could smell it in the engine bay. And geuss what, the ecu was SMOKED. It has 4-5 burnt traces, and one being one of the power leads for the ecu.

Whats weird is it didn't blow any fuses. It may not have been enough current to. I know it doesnt take much to damage a ecu.

We found 2 wires that were twisted together in the kick, someone didn't do a good job taking a remote starter out of it. Fixed those.

I found on this site that the O2 sensors shorting out will blow this fuse, and we did find a O2 sensor that shorted out on the car.

My question is has anyone heard of this happening? We are quite technically inclined, and I do wiring daily. So i know we can figure it out, just wondering if anyone has heard of this? OR what might have made the ecu blow without blowing fuses? I really dont wanna blow the new ecu.

Thanks in advance guys,
Alex

K04-S4

The appearance of the contact burn marks on the ECU housing suggest the housing itself shorted against the pins on the bottom of the ECU circuit board.

Is the housing bent concave at all or perhaps previously incorrectly installed in such a way that the housing had excessive inward pressure?

A6 4.2 Quattro

The housing looks fine, but that crossed my mind as well that it shorted outed out on the case its self.

It didnt look like it was installed wrong but it could have been a possibility!

Ecmbuster

No, that looks like reverse polarity. With the ECM connection OFF, test all pins and you should find only the battery and key ON wires should be alive. The rest are dead unless there is CAN activity (twisted pairs). Any other powered connections means that there is still a problem. Added insurance is a temporary 7 to 10 A fuse on the power circuits.

You can follow the damaged pins to the outer connector and with a schematic, find the origin of the damage. My guess is that the ECM is repairable.

A6 4.2 Quattro

Would you have a schematic? And we are trying to repair the ecu, I cant find a new ecu anywhere.

Ecmbuster

You should post the ECM part number. I don't have a board schematic, only the shop schematics.

A6 4.2 Quattro

Sorry, its a 4D0 907 558 S.

So the power leads on far left and far right sound be the only thing with power when the ecu is unplugged correct? None of the small pins should have power correct? I am going to test this, this afternoon.

Ecmbuster

I have a schematic that should help. The PCB is double sided so you better know what you're doing.

Besides that, this site doesn't allow for pdf documents in RAR format.

Lame.