My car has an error code that won’t go away

Q. I have a Chevy Aveo and I am having issues with the PO420 code. Both oxygen sensors were changed. The wire connections are good and I use quality gasoline. The car runs great and has 117,500 miles, but the check engine light still comes on. What is wrong?

A. The code is looking at catalytic converter efficiency. More than likely the converter just can’t perform properly, and that is determined by the front and rear oxygen sensors. You are correct that you wouldn’t notice any difference in engine performance, but the engine is producing higher than normal vehicle emissions. When you replace the catalytic converter, buy a quality replacement. I have seen bargain converters work for a while only to have the same PO420 code come back.