Every trip or two of over forty or so miles will inevitably cause the Check Engine light to illuminate on my N/A '96 850, which is otherwise very well-maintained and drives flawlessly. The code reader not only states "no codes" but when I check the status of the MIL it says that the light is off, even with it glowing away right in front of me. Running the process to turn the light off does in fact turn it off. But before long the light goes on and the process repeats itself. This has happened maybe six times in the last few months (I don't drive a lot--I take a commuter train to work).

In this and other forums this issue has come up a few times, almost always with newer, more computer-laden models. Some think it may be Volvo-specific codes, which I suppose is possible, but I thought that the Check Engine light was pretty much restricted to emissions items and not used for codes about power windows or door locks.

Any guesses, folks? Or better, has anyone got anything definitive? It's got me stumped...

Thanks!

I think you might have got it right-on! The odd thing was, I would have a check-engine light but no code; the reader would also indicate that the current status of the light was Off, but if I choose Reset, it turned the light off. I stopped by AutoZone, and their reader showed a PO133 code (may not remember it precisely) but it indicated an oxygen sensor switching slowly, which sounded like a vacuum leak, possibly. Indeed I found a deteriorated little rubber elbow on a vacuum line, so maybe that was it, or part of it. I did get a code soon afterward (which of course my reader said No Code!, but I deleted the code and it hasn't popped back up. I will continue to search for other vacuum leaks, but also I will search for a new code reader!

Thanks for your thoughts!

Try a different code reader, I had this issue on my 97 850. My set up on the laptop always read no codes and would not turn the light off. I thought it was a Volvo specific code or something. Then I had my daughter, who I armed with the Torque Pro App on her phone try it with the Bluetooth dongle (15 bucks) and it read the code and turned the light out. Code was an evap leak so nothing special. Not sure why, but hey, I fixed the issue.