DTC Troubleshooting: P0420 (67-1)

DTC P0420 (67-1):  Catalytic 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 Heated Oxygen Sensor ( secondary HO2S) (Sensor 2)
P0141:  Secondary HO2S (Sensor 2) heater

1.Reset the ECM/PCM, then continue to 2 through 5 to reset the readiness code.

2.Start the engine. Hold the engine at 3,000 rpm (min-1) with no load (in Park or neutral) until the radiator fan comes on.

3.Drive for about 10 minutes without stopping on a highway or freeway. Your speed can vary.

4.With the A/T in D position, M/T in 5th gear, drive at a steady speed between 80-100 km/h (50-62 mph) for 30 seconds.

5.Repeat step 4 three times. Between each repetition, close the throttle completely for 1-2 seconds. If the engine is stopped during this part of the procedure, go to 3 and do the procedure again.

6.Check for a Temporary DTC with the scan tool.

Does the scan tool indicate Temporary DTC P0420?


YES - Check the TWC. If necessary, replace the TWC.n


NO - Check for readiness code completion. If the readiness is complete, it was a intermittent failure, system is OK at this time. If the readiness is incomplete, repeat 2 through 5.n