you can reset the 4matic computer by removing battery power for 30 secs.try this first.you do not need a scanner to read off 4 matic fault codes stored in the cpu.when you start the car the 4 matic "brain"will flash out the code on the dashlight.just count the pulses.ive got a 90 4matic wagon never(touch wood)had a problem with the steering angle sensor but it maybe repairable.best of luck