Phantom dash lights - 2000 BMW 323ci

When I got the first smog check done on the car a couple of years ago (California), the ABS, Stability Control and Brake lights came on. The smog guy told me that after I drove the car, the computer would clear the messages - not. The lights come on and go off at random. My mechanic gets 3 error codes from the sensors (that would be 3 per tire). These sensors are not cheap and I hate to spend the money to replace them if the next smog check will blow them again and no one can tell me whether it will or not. Any ideas?

How about posting the exact error codes. Try Autozone or Advanced Auto Parts. Get the exact code not just their translation into English and post it back here. It likely will have a format like P1234.