4 Matic Control Unit

[William Brauer]

The 4matic is inoperative on my 92 300TE wagon with 140k.
Had some problems with the brake switch, replaced twice this year. The trouble lite went on again and when I got around to trying to get a code it would not produce one. My mechanic tried with the regular tester and it doesn't produce. We did replace the high voltage relay tied to a cold start problem and that had no effect. Does this mean the hugely expenseive control unit is shot? What do they sell for, new or used. Any other ideas? The car is in great shape, put a rebuilt trans in last spring but I don't think I can justify spending the money to get the 4matic back as I planned to sell the car as early as next spring to get something to tow a boat with. If its as bad as I think this little part will be 25% of the value of the vehicle, which I would have pated with with everything working for 8000. Any ideas or advice will be appreciated. I wonder if the same unit was used in the sedans etc for any length of time that would make them common used. The wagons are somewhat rare.

[Robert Goodwin]

Without a part number it is difficult for me to tell what is common to other cars without doing a bit of research. You might want to try www.beckmanntechnologies.com. They rebuild a lot of MB electronics. They may also do testing of your unit. You can check their web site or call them at 800-742-1021.

[William Brauer]

Thank You

[Hammer]

Without any codes set look for a hydraulic problem. Check fluid level in reservoir. If it's low pull the drain plug from the transfer case. If fluid gushes out you've found the problem! An internal seal failure in the transfer case.

[William Brauer]

The fluid level is good so I am hoping it is a hydraulic valve or better a sensor. Am in fact taking it in tomorrow for hopefully a decisive dignosis that will not break the bank to repair. I'll post the results.

[William Brauer]

After several shots at diagnosis, the problem with my 4matic was finally found to be a bad plug going into the rear hydraulic unit. Thankfully the problem was not a major part. As explained, the lack of a signal indicating hydraulic pressure apparently freezes the ECU in a failure mode, where fault codes won't generate. My wagon drove beautifully in several storms last week. I was amused to pass a newer 5 series BMW that was fishtailing wildly everytime the driver touched the accelerator. When these cars work they are fun to own!