itdoesitallroad

I had a bad engine surge that came anytime I accelerated. The 07 A8 would just heisitate and sputter untill I got in 6th gear and the rpm's remained low. The check engine light flashed while this was occuring. Parked the car for a couple of hours, turned it on and drove with no issues. Question: How long will the codes be stored in the car. I will be taking to dealer in 3 days because my warrenty is over in 4 days. Dealer said the codes may erase themselves if everything is back to normal.

jakematic

DTCs have reset counters as discussed here http://www.ross-tech.com/vcds/tour/dtc_screen.html

As I recall you have to go through X many drive cycles without a new DTC, and when it reaches 0 it resets.

itdoesitallroad

That's interesting. So I have a good chance that later this week when I bring the A8 to the dealer they may not find anything. And this is the last week of my warranty. So I need to hope the problem occurs again....that feels wrong.

volvopentaman

Engine DTCs have normally between 40 and 250 startups to reset themselves, depending on the faultcode. I'm quite confident that you do not reach those limits in a couple days in normal conditions. Try at least to minimize driving around with the car, especially starting and stopping the engine.

MP4.2+6.0

The CEL light may clear in as little as a couple of cycles. On my 2000 A6 4.2 which has a periodic fouling plug problem, if I get lazy and change or clean the plug but don't clear the codes with VAG COM the CEL light turns off in a few days anyway. The codes should still be in there in the ECU for quite a while as Volvopentaman mentions, but the light will turn off more quickly in the absence of a renewed fault. It will also hold the code as a (non) readiness reading for smog check purposes for 10 cold hot cold driving cycles. The CEL light being on is invariably an auto flunk on a smog check. In some states which read for readiness codes, it's a flunk too if all the tested systems don't report back as "ready" since they don't want people resetting the light right before a smog check where some of the issues take a couple of cycles (like the 4.2 vacuum hose issue for the air pumps for example) to turn it on in the fist place.

Having been through something like this with the TPMS and the Audi CPO warranty on my 2006 early this year, what the service manager told me and thus indirectly coached, was the light had to be on (TPMS in that case) for them to warranty it. If not, they would read the codes for a diagnostic fee but unless a particular sensor had outright failed, no warranty. Thus, the light invariably turned on another time (due to low batteries) and I just left it without resetting on the dash. That got me five new factory wheel TPMS sensors installed w/out charge beyond the basic CPO deductible. The engine is different in that I think it can self clear the CEL (light) even if still holding the codes. You do also have the emissions warranty (varies by state), but the language may say technically you have to fail a smog check first (as in, light on) and the extended emissions coverage still doesn't pick up a variety of possible problems even if they aren't formalistic on the smog check part.

itdoesitallroad

I bring it in on Thurs. and will let you know what they find.