1998 Chevy K1500 5.7L Engine P0420 Code After Replacing Catalytic Converter and O2 Sensors
I have a 1998 Chevrolet K1500 with a 5.7L V8 engine. I recently replaced both the catalytic converters and oxygen sensors. After clearing the check engine light, I drove approximately 5 miles and the P0420 code returned immediately. The vehicle has been running normally prior to this, but the recurring fault suggests an issue with exhaust system performance or sensor readings.
To properly diagnose this issue, you'll need a scan tool capable of monitoring live data, specifically the voltage readings from both pre-cat and post-cat oxygen sensors. The rapid return of the P0420 code indicates a likely problem such as open or shorted wiring, excessive voltage readings, or an underlying fault like a rich fuel mixture or engine running too cold that was not addressed during maintenance.