I have a similar problem with a 1994 E320 wagon. When the car is first started, the charging pump runs. After about 90 seconds or so, the pump stops and the ASR light comes on. The car is standing still, in park and at idle. The only code set was the brake light switch. Switch has been replaced, but the problem remains. The car has been to a very good shop and they are stumped. I have changed out the ASR control unit with two other units - no difference. I have checked fuses, wiring, relays and all connectors. This problem appeared after replacing the evaporator. I have replaced evaporators in at least 4 other 124's without a single problem. My friend is a seasoned, factory trained MB tech and the shop where I took the car is one of the best in the area. Switching the car off and restarting resets the ASR light, but the cycle just repeats itself. No codes have reappeared.

Does the charging pump run when you first start the car? When the pump quits running does the ASR light come on?

Tom