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 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 40 - 55 mph (64 - 88 km/h) for approx. 2 minutes, then decelerate for at least 3 seconds with the throttle completely closed. Then reduce the vehicle speed to 35 mph (56 km/h), 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.

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

Tailpipe Emissions Test
1. Start the engine. Hold the engine at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on, then let it idle.
2. Connect a tachometer.
3. Check and, if necessary, adjust the idle speed.
4. Warm up and calibrate the CO meter according to the meter manufacturer's instructions.
5. Check idle CO with the headlights, heater blower, rear window defogger, cooling fan, and air conditioner off.

On Canadian models, pull the parking brake lever up, start the engine, then check that the headlights are off.

The CO meter should indicate 0.1 % maximum.