A6 / S6 (C5 Platform) DiscussionDiscussion forum for the C5 Audi A6 and S6 produced from 1998-2004
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The problem is now solved, although there were a few quirks along the way, hence the post.
The symptoms were as posted by others. Running fine, with CEL light on (for a know issue with the secondary air pump), suddenly no start.
STEP 1: scanned for new codes. Nothing new, Cleared the old codes.
STEP 2: Checked fuse #28. No power on input side.
STEP 3: Powered the output side with 12v, fuel pump runs fine.
STEP 4: Removed drivers side knee bolster panel to access relay rack.
STEP 5: While holding Relay 4 (fuel pump relay), turned on ignition. No click heard of felt.
STEP 6: Replaced relay.
STEP 7: still no start ....
STEP 8: check #28, no power on input side.
STEP 9: much time reading forums for answers ... nothing jumped out as a solution.
STEP 10: incantations to the Budweiser god ... (made me feel better, 90 degree NC heat)
STEP 11: Hooked up HD starter booster in case engine crank RPMs were too low
STEP 11: Broke out VAG 5053 and scanned for crank position indicator (engine group 01): Clear output signal following engine crank speed (160-200 rpm).
STEP 12: Cranked engine for a good 45-60 seconds, and she slowly began to fire intermittently ... much black smoke from the exhaust, which quickly cleared after 30 seconds of smooth idling.
Now, when the key is turned, I hear the fuel pump prime (as usual) and she runs just as before.
I have no idea why she eventually fired, but I had seen reference to others who had to hard crank after they had changed the FP relay: maybe when I ran the FP from the 12v line, I flooded the engine ...
Anyway, another couple of Budweiser's were consumed in thanks to a problem solved!