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.