I have a 99 s70, non-turbo- 116,000 miles. I have had a intermitent check engine light for PO420( converter effiency below threshold L ) for several months. recently it has stayed on steady. Engine runs excellent and there hasn't been any change in performance. Should I suspect one or both of the O2 sensors or should I be looking at replacing the converter?

Thanks in advance for any suggestions.

Rick

 

Does the car misfire?
Any other things happen lately?

 

A few days after my post I reset the error code just before a 350 mile drive . The light hasn't been on in the 750 miles since that trip.

 

Let sleeping dogs lay then. LOL