I picked up a '92 W124 4Matic wagon over the weekend; at its age and mileage I hardly expected the system to work. However, it's not in "test" mode and I have driven it 500 miles since purchase without issues.

The car is definitely tired with over 200k miles, but it seems to have been cared for with no rust to speak of and nearly perfect (green!) leather seats.

A friend and I took the car to a grassy area. The 4Matic does not work.

The ABS light is on. I understand that the 4Matic system uses the ABS sensors to function, so maybe this is a place to start.

Does anyone know how to diagnose the system - can I get the ABS light to "flash" codes?

And before we get into all this, yes, I know that the W124 4Matic system is no good and unreliable, etc etc. I did not buy the car thinking I could get it working, but it sure would be a novelty if I could.