P0420

DTC P0420: 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.
- Before you troubleshoot, record all freeze data and review the general troubleshooting information.

P0137, P0138: Secondary heated oxygen sensor (secondary HO2S (Sensor 2))
P0141: Secondary HO2S (Sensor 2) heater

1. Reset the ECM, then continue to steps 2 through 5 to reset the readiness code.
2. Start the engine. Hold the engine speed at 3,000 rpm without load (in neutral) until the radiator fan comes on.
3. Drive on a highway 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, go to step 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 three way catalytic converter (TWO. If necessary, replace the TWC.

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 steps 2 through 5.