I have a 1993 940 turbo with about 170k miles. Car runs perfectly well. Only problem I have noticed is that the cruise control didn't seem to work the last time I drove the car. I'l have to investigate that and see if that would give me a CEL.

The check engine light has come on but I am reading a 1-1-1 in DTM-1 when testing the A section for codes. I have complete instructions for testing for diagnostic codes (Volvo Owners Club pdf) and have tried checking the other DTMs without figuring out much. I was hoping just to find the reason for the CEL, but I guess it's not that easy. (Yes, it's the CEL and not the Service Interval reminder.)

So here's a question: If I have no codes in DTM-1 and read a 1-1-1, what things can I eliminate? The Socket 2 codes seem to cover all of the usual suspects, but there's only a 1-1-1 there.

This might lead you astray, but the one system I know is not as it should be is the EGR system. I had a bad hose there and capped the to vacuum intake ports associated with the hoses going to the canister. I never got a fault or noticed any problem and just left it that way, and it has been like that for about 3 years without a code, so I don't think that's the reason.

So, what gives you a CEL if not something that is caused by a DTM-1/Socket 2 error? Hints? Suggestions? True Wisdom?

 

First, the OBD1 is far from perfect, it's better than nothing but you can't rely on it--OBD2 even is not completely perfect either for that matter. Have you tried resetting the CEL both ways, disconnecting the battery and through the box? If still no success, may be the EGR mod you have is affecting the light but not the code reader: it has happened. If it runs well, leave it alone, unless you need to pass emissions somewhere, then you have a problem. The cruise control should not set off the CEL unless it is vacuum hose related...

 

Are you connecting to the correct pin for engine codes?

 

Socket 2 should be correct for engine codes, I think.

 

I found a much better description of how to check all of the various modes. I'll give that a shot tomorrow and report back.

OBDII and Diagnostic Codes: 1992-1995 Volvos
https://www.matthewsvolvosite.com/read-codes-volvo-850