P0420

NOTE: This DTC requires two "trips" or two driving cycles unless the SCS service connector is connected.

P0420 - The scan tool indicates Diagnostic Trouble Code (DTC) P0420 - Catalyst system efficiency below threshold.

Description
This system evaluates the catalyst's capacity by means of the HO2S (Primary and Secondary) output during stable driving conditions. If deterioration has been detected during two consecutive driving cycles, the MIL comes on and DTC P0420 will be stored.

NOTE: If some of the DTCs listed below are stored at the same time as DTC P0420, troubleshoot those DTCs first, then troubleshoot DTC P0420.

P0136, P0139 - Secondary HO2S
P0141 - Secondary HO2S Heater

Possible Cause
- TWC Deterioration
- Exhaust system leakage

Troubleshooting Flowchart: