The 2022 GMC Savana's check engine light with P0420 indicates reduced catalytic converter efficiency. This affects emissions compliance and requires systematic diagnosis to identify the actual cause.
Catalyst Efficiency Monitoring
The ECU monitors catalyst health by comparing upstream and downstream oxygen sensor readings. A healthy converter significantly changes exhaust composition; a failing one passes exhaust relatively unchanged.
Causes of P0420
Catalytic Converter Wear
Converters degrade over time. Commercial use with frequent cold starts and idle time can accelerate wear.
Oxygen Sensor Problems
Faulty upstream or downstream oxygen sensors provide incorrect data, potentially triggering P0420 with a good converter.
Exhaust Leaks
Leaks allowing air into the exhaust affect oxygen sensor readings and can cause efficiency codes.
Engine Running Issues
Misfires, rich/lean conditions, or other engine problems send improper exhaust to the converter, potentially triggering P0420.
Systematic Diagnosis
Don't automatically replace the converter when P0420 appears. Proper diagnosis prevents unnecessary expense.