P0420

DTC P0420: 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 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. Drive for about 10 minutes without stopping on a highway or freeway. Your speed can vary.
4. With the transmission in D5 position ('99 model: D4 position), drive at a steady speed between 50 - 62 mph (80 - 100 km/h) for 30 seconds.
5. Do step 4 three times. Between each procedure, close the throttle completely for 1 - 2 seconds. If the engine is stopped during this procedure, go to step 3 and do the procedure again.
6. Check for the three way catalytic converter (TWC) test result with the scan tool.

Does the scan tool indicate FAIL?

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

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