DTC Troubleshooting: P0420 (67-1)

DTC P0420 (67-1):  Catalyst System Efficiency Below Threshold

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


P0137, P0138: Secondary HO2S (Sensor 2)
P0141: Secondary HO2S (Sensor 2) heater

1.Reset the ECM/PCM.

2.Start the engine. Hold the engine at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on.

3.Test-drive at 80-88 km/h (50-55 mph) for about 2 minutes. Then decelerate for at least 4 seconds with the throttle completely closed. Then accelerate to 88 km/h (55 mph), and try to hold it until the scan tool indicates FAIL or PASS as the TWC test result.

Is the test result FAIL?


YES - Check the three way catalytic converter (TWC). If necessary, replace the TWC.n


NO - Intermittent failure, system is OK at this time.n