CKonstantin

I have a May 96 E300, from time to time my check engine light comes on, I have a small OBD II scanner,it detects the protocol as KWP-2000, but it always says No codes, when I try to erase them it says Error, I tried another OBD II scanner and it could not connect at all...
A local shop has OTC scanner with 38pin plug it scans the car no problem and can Read and Erase codes from most modules...

Any ideas why it would happen and what can I check for, it's a California style OBD II plugs with 1 permanent power 2 grounds and 1 data wire, what can I check and how?

CKonstantin

If I was to test the DATA wire, what am I looking for, voltage, pulses, ground?
Would it be safe to plug a multimeter or a diode tester to it?

RichardM98

Did you try using the scanner on another car? Since two scanners didn't work on your car perhaps the OBD connector has an issue.

CKonstantin

Yes both scanners work on other cars, yes connector clearly has an issue which I would like to pinpoint, scanner powers on, so there is power and ground, which I independently confirmed with a multi-meter. What I would like to know is, which way to go about testing the data wire, which transmits the data from ECM to the scanners, because one(more expensive) scanner could not connect at all, where as the cheaper Chinese version appears to connect but reports no codes being stored, and displays an error message if you try to erase them.

RichardM98

I don't have a direct answer but I know the same data is available on both connectors. You might want to post in the Tech Help section of the peachparts site. Members of pre 96 models have tricks to read individual values from the 38 pin connector since they don't have the ODB connector under the dash. I think there is some sort of home-brew tester but it seems like you would be able to make one.

Hope that helps some.

CKonstantin

From what I've read about those connectors, they do not share the same wire, as people who have European cars, without OBD II plug; bought the 38pin to OBD II adapter did not manage to read out any codes. As far as I know pre96 vehicles used pulses to transmit the codes so you can read them out with fairly basic testing equipment, like a diode tester for example, by grounding the pin, or some similar method; post 96 vehicles however use data stream and such communications cannot be read out with 'home-brewed' testers.

RichardM98

Thanks for the explanation. Since it wasn't an issue for me I didn't dig too deeply into it.