Problems with '97 A8 4.2 Quattro Tiptronic

[pakman]

I was away for a couple of weeks and came back to discover that the A8 wouldn't start. I boosted the battery to get it running and then set of for a short trip to charge it up a bit. About 2 minutes down the road the car started coughing as it shifted into 2nd (automatic box) and then the 'Cat' warning symbol came on. I slowed down to a crawl to find out what's going on and the car then gave up completely.

It no longer starts up but the engine does turn over, and the cat light is still on.

Could the battery going flat have affected any electronic settings or the immobiliser/ingnition code? I've tried all the keys and left the ignition on for a few minutes to see if it recodes itself but it doesn't help.

Any suggestions?

Thanks.

[JimR]

I'd yank the battery and test it, to start. And VAG-COM the car for DTCs.

[ttuling]

The immobilizer should shut the engine down cleanly with no coughing or 'Cat' light (which presumably indicates an engine management fault). Although if the car has a non-Audi immobilizer which disables the fuel pump, it might cause this problem.

As JimR said, checking for trouble codes with a tool such as VAG-COM is likely the next step. I can't think of what kind of problem caused by the dead or boosted battery would appear only after two minutes of running.

Not that these are likely to help, but you might check fuses including that for the fuel pump, and you might disconnect the battery for several minutes then reconnect it in case a computer got off to a bad start. There is a prescribed minimum time to wait after turning on the key before cranking the engine when the battery has been dead. It should be in the manual, which I don't have at hand.

Tom