Greg5OH

Didnt have a chance to scan codes yet or really dig into the issue.
Long story short, swapped a new motor into this 07 A6 4.2
Now when I plug the battery in, within 5 seconds the fans turn on full bore
Sometimes they turn off when I open the driver door, sometimes not.
Then sometimes will come on for 30 seconds randomly, sometimes for 5 mins, sometimes wont come on for an hour....
I replaced the relay under the ECM with a known good spare but still doing it.
Anyone have something similar happen?

Otherwise car starts and runs fine.

Greg5OH

Greg5OH

So I dont know if something hokey is going on, but..something hokey is going on.
FIrst off, when I got the car, someone tinkered with the wiring under the right (passenger) e box.
This a BVJ engine mind you.
oam wiring diagram calls for a J271 relay which is the ECM power supply..I only have a 373 under there, and I see a red/green wire has been cut with a purple wire splitting off into 2 643 relays, and then 2 mroe small purpel wires branching into 1 OEM looking gold connector to the power distribution block... These 643 relays dont exist on any wiring diagram...

so when the fans come on..both turn off when I pull one of these 643 relays off..

However what is most concerning, is as I was pulling these two relays in and out, i later went to go start the car...and now the PRNDL is all lit up, and the ECM is not communicating at all...continuity tested all fuses, all good...
did one of the 643 relays just stick open on me? Going to test both relays tomorrow on the bench and see.... need to pull some more relays from the junkyard.

I have a c6 s6 here, and i checked under the right box...those relays dont exist, no hokey cut and spliced wiring...jhust the one relay at the bottom (dont remebr if it was 271 or 373)...


So frig, now I gotta see if the ECM is even getting power. If its not..then trace it back to where it should be...
if it IS getting power...then im facked.

Looks liek connector 94, pin 92 and 69?

[img]https://imgur.com/4dEpOcb[img]

beep-beep

The simplest source of this problem is the coolant temperature sensor is not working correctly or there is air around it and it does not read temp right.

Greg5OH

ECT sensor appears tobe working correctly, I can (was) able to monitor the temp in VCDS and stabilized around 90C. This is with engine running though, I did not monitor with engine off..

Right now my biggest issue is the lack of communication from the ECM

Greg5OH

I am getting 12v at pin 69, white/black wire so ECM should be waking. I believe it is as I am getting 2.5V on the CAN lines. No picoscope with me at the moment so I cannot confirm the message, but it is sending something out.
Rechecked the fuses in driver under hood ebox, dash left and right and trunk-all good.

According to erwin and mitchell, the only relay in the right compartmenet under the ECM, is the one for 2ndary air inejection, and also poweres the evap leak detection pump. The wire colors goign to the relay confirm this in vehicle.
The ECM relay in the diagrams resides in the left box with 2 other modules. The wire colors physicaly correspond to the vehicle. the black/white power wire for ECM is on the left side relay, J271.

Just for fun, I decided to swap the relay under the ECM, labeled in diagrams and physcially...as the SAI pump...welll...communication restored, she fired up.
Im happy..but perplexed.

Now to tackle the fan issue. e
To me, it looks like the relays were simply added on. Again these relays dont exist in any wiring diagram. The power wires are interrupted and ran to the relays, and one side is getting power from main fuses, the other looks like its triggered by the actual fan trigger wire to which it is butt crimped on to...

Greg5OH