Check Engine Light

Sometimes, but not all the time, my, “Check Engine Light” comes on. When on, it’s on steady and does not blink. My local auto parts store scoped it out as trouble code P0421. My maintenance manual lists code P0420 as, “Catalyst system efficiency below threshold”. I bought the car used with some prior issues, including one loose spark plug that I needed to replace plus some other work that I needed to do. It’s a four cylinder and, actually, I’m thinking it does run quite well and it did just recently pass Washington State emissions. I think there are sensors on either side of the catalytic converter (and, hopefully not the converter, itself) that may need to be replaced but am not sure. My fuel consumption seems to be OK. My real concern is will I harm the engine if I just do nothing and keep on driving with that pesky light coming on occasionally?

Would this happen to be a 1996 or 1997 car?

Proper diagnosis would include testing of the O2 sensors before and after the catalytic converter. If one or both O2 sensors are going you will get a “system below threshold” code. It does not necessarily mean the cat itself is bad.

Have someone test the output from the O2 sensors to see if they are within range.

It’s a 2001 626.

Will do. Thank you. Bob