I know almost all cars (nissan, honda, volvo etc.) you can run diagnostics and see if a there is a problem with a sensor, without any extra test equipment. Just the check engine light, and watching how many flashes you get.

I went down this same research road and wasn't pleased with what I found. There are two types; Federal and California. As I understand, the California version does have a somewhat complete diagnostic system and the codes can be read by jumping something on the fuel pump relay. The Federal models, which is what I have, have very little diagnostics. There are a few trouble codes that can be read by measuring the duty cycle at the diagnostic connector. There are only a few subsystems that are indicated as a problem if present.

I expect that you will need the MB manuals to do any extensive troubleshooting on this car.

Please report what you find so that we can all learn from it.

Good luck,

I went through the same thing recently. A while ago a
salesman at MBZ dealer told me that most cars brought
into the West Coast are California certified and I do
have a basic code reader by the battery. Are you on the
West Coast? Stevebfl said "You must have a California car as the mounted light only appeared on 93-95
Federal models."

He is correct in his assessment.

Gary