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2001 Volvo S40 -- Check engine light at 48 MPH

I can set the check engine light on my 2001 Volvo S40 at 48 MPH. It will set a code “poor catalytic converter performance.” (I forget the exact number.) The check engine light will reset on its own in a week or so. I try to avoid that speed.

My drive to/from work is mostly at about 45 to 50, so I’d like to get to the bottom of this one.

Two ideas: is there a vibration at this speed? Is the car going into overdrive at that speed? A recent visit to a shop did not find any transmission codes.

Would an exhaust gas analyzer tell that the converter IS working? Also, can driving with the PC that captures the data bus activity show WHY the code was set? Maybe my mixture goes nuts at that speed.

I might just use Black Tape as advised on the radio show, but I think my gas mileage goes bad when the light is on.

Ray in Rochester, NY

I doubt you gas mileage changes at all when the light is on. If the light goes out on its own, then the problem is intermittent and likely not a big deal until either the light stays on, or starts flashing.

Getting more specific info, and a “fix” on an older Volvo is going to get expensive.