2000 Audi A6
4.2 Quattro,
Tiptronic,
119,000 miles
Codes: Don't have them with me, will update the post.

I took my A6 into Pep Boys to have them change the battery ( I know, bad idea). When I gave them my car, it was running fine, except it was taking a while to turn over (had the old battery tested and it needed to be replaced). As soon as I fired up the car after changing the battery it ran slightly rough at idle, and the check engine light came on (light was solid, but flashed every 3-5 miles). However, car feels good at speed, and doesn't lack power.

I took it back to Pep Boys and they pulled codes which stated the following:
1) Cylinders 1-4 misfiring
2) Catalytic converter malfunction
Of course they didn't believe me that the problem started exactly when the battery was changed (I swear!).

I took it to my mechanic and he pulled the following additional code:
1) Camshaft position sensor malfunction
He then replaced the sensor, but it didn't help the problem.

I'm at a loss - I know this problem happened when the battery was changed, so I'm thinking it fried something in the electrical system: ECU? Ignition Coil Packs?

I'm at a loss, please help!

 

I am having the exact same problem. Replaced battery, car went to crap. Car runs terrible, engine light flashing 27, sputtering terribly, traction control light comes on intermittently. Towed to mechanic. Has had it for two days. Doesn't know what is wrong. About ready to just sell it. Help!

 

When replacing the battery, it can reset the ECU especially if the positive terminal touches the body and grounds out.. The procedure I follow when replacing the battery or having left it disconnected for a while is this. Insert the key and turn on the ignition but do NOT try to start the engine. Let it sit for 15 or 20 seconds in the "on" position. THEN turn the key to start the engine. It will stumble at first but catch on a run. The ECU is "relearning" to run the engine since all of the previous data stored is gone. This is perfectly normal. Sometimes it will trip an error code but you can go in a clear them after driving the car for a day or so. I've run into other cars and trucks that the ECU takes a day or so to finally "relearn" to make the engine run and idle properly.