300E 4matic - Returning to Function Mode
 

My brother's '92 300E 4MATIC system was placed on test mode for about 2-3 months, on the advice of our Mercedes tech (trying to prolong the system's usefulness). The system worked fine before putting it in test mode with the exception of some minor vibration when running at low speeds with the wheel sharply turned. Upon switching back to "Funktion," the rectangular "4MATIC" light on the dash stays lit and the system remains disabled. The car seems to be driving fine on the rear wheels. (Of course, he waited until we got a foot of snow before trying to reactivate the system). We've tried removing the positive battery cable for half an hour, 2-3 times, with no success. Does this mean that a problem developed with the 4MATIC while it was running on "test" mode, or does someone know another trick that might get the thing activated? We're in the middle of some midwestern winter weather, so any advice would be appreciated.

Any time the battery is disconnected the system must be re-activated by reinitializing the steering angle sensor.

Turn the steering wheel lock to lock to reset.

Thank you very much for the information. I relayed this to my brother. He said after getting home last night, he tried turning the wheel all the way left, and then all the way right. The 4MATIC light stayed on. Is there any particular procedure to follow? Just start the car and turn the wheel lock-to-lock once?