Fault code P0420 - 2002 Oldsmobile Silhouette

This Code means your Catalytic converter is not working like it should. You may have a problem on Bank 1 or the O2 sensor is giving you false readings. At a minimum you should either replace or have the O2 sensor tested to verify that the Catalytic converter is working properly.

If the O2 sensor is accurately performing its job, then have the engine scoped before replacing the Catalytic converter.

You should have received a defect Code for other components which could foul the Catalytic converter. This is why I recommend getting the engine scoped. If other defects were corrected before you purchased this vehicle, then the Catalytic converter may be able to recover by itself.

The Converter costs so much that you should verify things like low compression on the number 1 bank.

Code P0420=EVAP system - Large leak....most common problem is a bad gas cap, try that first if that does not cure the problem then check the fuel tank vent lines on the top of the fuel tank for crackes if the lines look ok most probally need to replace the EVAP vent valve on the top of the fuel tank....good luck