2001 A6 4.2 Quattro / Tip / 96k miles.CEL was on when I bought the car 9 weeks ago, dealer (not Audi dealer) agreed to fix it. Original code led mechanic to secondary air injection (sounded like static on the radio from inside the cabin, but radio wasn't on) - replaced a couple of loose/rotted air lines, don't hear the sound now.
But, the CEL came back on after driving 30 miles. Dealer sent it to Audi, diagnosed & replaced Bank 1, #1 O2 sensor. CEL back on after 30 miles, Audi again diagnosed it as the same sensor, replaced it again, and, yes, the CEL is back on (haven't pulled codes yet).
Question: Any ideas on what all these "mechanics" are missing? Hard to believe Audi can't figure this out. (or is it?)

Question: did I buy a dog? Background: 1) originally, car also had the ABS light on, dealer said Audi replaced the ABS module. Wrong - turned out the steering angle sensor and module needed replacing (had it rebuilt), cost me $900 and theypaid labor. Seems OK now. 2) Front left control arm was bad, I paid $300, they paid labor. 3)Couldn't tell if timing/ serpentine belts had been replaced, had them do it - I paid $700 (TB kit w/ water pump), they paid labor. 4) spare wheel is cracked, won't hold air. 5) used headlight washer one night, cover came off 6) headlight adjustment service light is now on, Audi says it'sheadlight motor. 7) cruise doesn't work.
Afer saying all this, I hate to admit that I love driving this car, but it's 65 miles one-way to these guys, andI just can't do this any more! Sorry for the whine - I'll go buy some cheese.

 

I think this may be related to a vacuum leak. I know that the secondary air injection code I had was a disconnected vacuum line, and you mention that you had some rotted lines and that the cruise doesnt work (another sign of a vacuum issue). Do you have the actual code? Hard to believe they would miss that though.

 

Thanks. I will get the actual codes, but don't understand why a vacuum leak would keep throwing an O2 sensor code, or why a certified Audi mechanic just keeps replacing O2 sensors without checking on something else. Doesn't appear to be givng secondary air injection codes now, just O2 sensor.

If I keep this car, my next purchase will be the Bentley manual and the Vag-com setup.

One really depressing thing- I have a friend(?) who owns a small independant Audi/VW repair shop, has been an Audi mechanic for 20 years. He won't even touch a 4.2 because "they're too problematic and expensive". Great.

 

He's only replacing an 02 sensor because 90% of the time a 02 sensor fault means the sensor is faulty. If the 02 sensor is throwing a fault constantly its either the MAF sensor or a vaccum leak is present.
The cruise control should have a fault code for what the problem may be, most commonly a vaccum leak, or faulty CCM module.