The 2023 Ram ProMaster City's P0420 code indicates reduced catalytic converter efficiency. This affects emissions compliance and may indicate converter wear or related system problems.
Catalyst Efficiency Monitoring
The ECU compares upstream and downstream oxygen sensor signals. A healthy converter shows significantly different readings between sensors as it treats exhaust. Similar readings indicate reduced efficiency.
Causes of P0420
Catalytic Converter Degradation
Converters naturally degrade over time. Commercial use with frequent cold starts can accelerate wear.
Oxygen Sensor Issues
A faulty downstream sensor can report incorrect data, triggering P0420 even with a good converter.
Exhaust System Leaks
Leaks allowing air into the exhaust affect oxygen sensor readings and can trigger efficiency codes.
Engine Running Problems
Misfires, rich/lean conditions, or other engine issues send improper exhaust composition to the converter, potentially causing P0420.
Proper Diagnosis
P0420 doesn't automatically mean converter replacement. Systematic diagnosis prevents unnecessary expense.