Hi,

I have a 1988 300E (Canadian Version, i.e. no switch/LED at the diagnostic plug next to the battery) and my car is losing power. Everything has been changed (spark plugs/wires, O2 sensor) etc....

Still, no improvement. I would like to be able to read what fault code (if any) has been set in the computer (and to reset them). I've read that I can build a LED counter (which uses pin 1 and 3), however, pin 3 on the diagnostic plug (next to the battery) doesn't have anything in it (it's just a hole)....the pins that are available are pin 1, 6 and 7.

Any advice would be greatly appreciated.

You also can press the button right next #1
key on or engine running press button and hold 2~3 secods count how many blinks if blink three times (code #3) if blink 5 times
(code #5)......after you read all the code
or after repair is done press button again hold it for 8~10 seconds to reset check engine light.

------------------
MB STARS Master Guild Technician,12 years MB tech
5 years independent shop owner

Thanks for your reply...However, I don't see any button/LED on the diagnostic plug....

Please help. Thanks.

Your car has the same fuel ECU as US cars. In 1988 there wasn't any hard codes stored in ECU. The only diagnosis is with Lamda meter (on/off ratio). If you get a fixed reading there is a fault. The computer is the least likely problem.

Is there a way for me to measure the lambda with a multimeter? How do I know if it's ok? And it's not ok, how do I adjust it?

I've read from the mercedes mailing list that if the O2 is bad, the computer will put the car in a conservative/limb home mode (which is why the car is so slow, I suppose). When the computer is reset, the car will be back to normal, but the computer will be back in the conservative mode after about 20 mins - since the O2 hasn't been replaced yet. I've already replaced the O2 sensor, so, according to this theory, I should just reset the computer and the car will be back to normal, right?

Is there any truth to this theory?

Thanks.

[This message has been edited by E. Lee (edited 08-04-1999).]