P0420

DTC P0420: Catalytic System Efficiency Below Threshold

NOTE: If some of the DTCs listed 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, then continue to step 2 through 5 to reset the readiness code.
2. Start the engine. Hold the engine at 3,000 rpm without load (in neutral) until the radiator fan comes on.
3. Drive for about 10 minutes without stopping. Your speed can vary.
4. With the transmission in 4th gear, drive at a steady speed between 50 - 62 mph (80 - 100 km/h) 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, repeat steps 3, 4 and 5.
6. Check for a Temporary DTC with the HDS or a scan tool.

Does the scan tool indicate Temporary DTC P0420?

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

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