W124 4Matic - anyone an expert?
 

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.

There is a diagram somewhere to make a LED / resistor / switch / banana plugs that will work on all systems ( ABS / engine and so on ) If you have anything that uses an LED you can get parts.

In general, most ABS failures regardless of car seem to come down to speed sensors. The area around the sensor rusts lifting it off the mount reducing signal. The wire flexes and breaks also causing a problem.

I'm wondering if the transfer case is on / off or modulated to engage the front drive shaft? If the electrical system is unfixable i'd be real tempted to use a switch 4WD ON / OFF then drive it like a part time 4wd truck. ( 4 wd off on dry pavement )

Dont listen to the naysayers early 4-matics are awesome! With the ABS light on I'd be most suspect of the O/L relay. Start there.

It is quite easy to read the diagnostic trouble codes and then reset the system. Using the diagnostic port by the battery, jump the number 1 and number 5 for about 3 seconds with the car on, then read the flashes of the 4matic indicator light on the instrument cluster to get up to 9 different codes. After reading the codes, you can reset the system by jumping the same ports for about 5+ seconds. If it works okay, you're done. Simple as that.