Well this is starting to get a bit discouraging. I now have three codes setting the MIL light off and a fourth code to boot. It has been running a little bit rougher than normal spanning multiple tanks of gas though there is no engine misfire that I can feel at any speed or idle. MPG is still great. 2003 A6 Avant 3.0 with 104k miles. First two codes I've had since the timing belt service was done - the MIL would come on and go off for awhile, but then stayed on continuously:

16805 - Warm Up Catalyst; Bank 1: 001 Upper Limit exceeded MIL ON
16825 - EVAP Emission Control Sys: Incorrect Flow: 002 Lower Limit exceeded

Now, I'm getting
16684 - Random/Multiple Cylinder Misfire Detected: 001 Upper Limit Exceeded MIL ON
and
16690 - Cylinder 6: Misfire detected: 001 Upper Limit Exceeded MIL ON

Plugs were changed about 15k miles ago. Coil packs have all been changed and are all the same rev. I have not yet changed the wires.

That being said, I'm guessing that number 6 cylinder has a problem (there is an ongoing coil pack recall for this vehicle - not sure if they have a new rev for them or not). But will a misfire on one cylinder on the 3.0 cause the random code as well? I know it does for the 1.8T in my A4 as one coil pack change got rid of both codes 30K miles back.

Regarding the cat, is it true that once they go bad that's it or can they be borderline for awhile with the CEL going on and off?

Can the EVAP problem cause the Cat code and or the misfires?

Any opinions welcome.
Thanks

 

16684 - Random/Multiple Cylinder Misfire Detected: 001 Upper Limit Exceeded MIL ON
and
16690 - Cylinder 6: Misfire detected: 001 Upper Limit Exceeded MIL ON

If you started receiving those soon after your timing belt was changed, bring it back to them and ask them to check if the belt was timed correctly. I know I got mine changed and once i got it back my CEL would blink intermittently and it turned out that they didn't time my belt correctly, they quickly fixed it and was g2g.

 

Why don't you move the #6 spark coil to another location to see if the misfire code follows. I have a hunch that you may have a bad #6 spark coil.

Could be a problem with timing belt, but I'd look at the simplest cause first.

 

Yeah, I guess there is no rule that says a replaced coil pack can't go bad again. Been about 10k since the T-belt change and still runs very well, just a very slight rough idle.

Thx

 

hmmm, my experience with bad coil packs is a very rough running engine under power. Maybe that's not it after all. But, still no cost to move the coil to another plug.