P0420 Fault on 2002 Chevrolet Grand Prix After Catalytic Converter Replacement
My wife's 2002 Chevrolet Grand Prix developed a clogged catalytic converter last year. The issue initially manifested as poor engine performance, followed by an EGR fault code. I replaced the catalytic converter with a generic unit at Meinake, and after that, the EGR code disappeared and the vehicle ran smoothly. However, about two weeks later, a P042
Replace the other O2 sensor — I've frequently seen the P0420 code when only one O2 sensor is replaced without updating the corresponding downstream sensor. Contaminants from one sensor often affect the other. If the check engine light remains on after this, it may be worth trying a higher-quality catalytic converter that isn't necessarily OEM but offers better performance than what was installed at Meinake. Good luck and please keep us updated!