2000 Buick LeSabre 3.8L P0420 Fault Code Explanation and Solutions
I own a 2000 Buick LeSabre Custom with a 3.8L engine. The vehicle had been parked and not driven for approximately six months. After changing the oil and driving it for about one hour, the check engine light activated. A diagnostic test revealed fault code P0420. I'm seeking clarification on what this means—should I replace the oxygen sensor or the catalytic converter, or is there another possible cause? Any guidance on next steps would be greatly appreciated.
It's recommended to monitor the O2 sensor readings and compare pre- and post-catalyst waveforms to assess performance. A long drive may help bring the catalytic converter up to operating temperature, which is unlikely but worth attempting as a troubleshooting step.