Hi there.
I have a a4 1.8t (B5) 1996. Had a problem with the starter motor, which i have fixed. but whilst it was off the road the battery went flat. When i tried to start it it would not start because of the flat battery. I took the battery off and changed it, put it back on the car, it started and ran fine. Then when i turned it off and tried to start it again it started fine, ran for 2 secounds then stoped and a red light came on with a key on. Started it again and agiain it ran and stopped. I disconected the battery and left it for a few hours. when i came to look at it again it started and ran fine, turn it off and same problem again. If i disconnect the battery and leave it for about 30 mins, reconnect and start, it runs fine, turn it off, start it, and back to the same story. Someone said it could be the key reader, i have used both keys but woudn't it not start at all?. I dont want to scrap the car as its a good car but its not worth sending it to audi's to be fixed. Any help in this matter would to very helpfull. Cheers

 

The key light is the immobilizer light. It isn't reading your key, or your key isn't recognized.

The two most common reasons for this problem are:
1. The reader coil in the ignition switch is bad.
2. The key isn't programmed into the immobilizer.

from the second post here:
https://www.audiforums.com/forum/aud...-symbol-17579/