DTC Troubleshooting

Control System DTCs

DTC Troubleshooting: P0420

DTC P0420 : Catalyst System Efficiency Below Threshold

NOTE:
* Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information How To Troubleshoot The Fuel And Emissions Systems.
* If some of the DTCs listed below are stored at the same time as DTC P0420, troubleshoot them first, then recheck for DTC P0420.
- P0137, P0138: Secondary HO2S (Sensor 2)
- P0141: Secondary HO2S (Sensor 2) heater
- P0300: Random misfire
- P0301, P0302, P0303, P0304: No. 1, No. 2, No. 3, No. 4 cylinder misfire detected

* Poor quality fuel may cause this DTC.

1. PGM-FI system check 1:

PGM-FI system check 1
-1. Turn the ignition switch to ON (II).

-2. Clear the DTC with the HDS.

-3. Start the engine. Hold the engine speed at 3,000 rpm without load (in neutral) until the radiator fan comes on, then let it idle.

-4. Test-drive under these conditions:
* Engine coolant temperature (ECT SENSOR 1) above 158 °F (70 °C)
* Transmission in 5th
* Vehicle speed between 45-75 mph (70-120 km/h) for 5 minutes or more with cruise control set
* Vehicle speed between 55-75 mph (90-120 km/h) for 10 seconds, then decelerate (with the throttle fully closed). Repeat this three or more times
* Maintain the vehicle speed at 55 mph (88 km/h) for 5 minutes or more with cruise control set

-5. Monitor the OBD STATUS for DTC P0420 with the HDS.

Does the HDS indicate FAILED?
-YES- Replace the WU-TWC Warm Up TWC Removal and Installation, then do the repair verification.
-NO- If the HDS indicates OUT OF CONDITION, go to step 2 on this step and recheck. If the HDS indicates PASSED, intermittent failure the system is OK at this time. If the HDS indicates EXECUTING, replace the WU-TWC Warm Up TWC Removal and Installation, then go to step 2.

2. PGM-FI system check 2:

PGM-FI system check 2
-1. Continue test-drive until a result comes on.

-2. Monitor the OBD STATUS for DTC P0420 with the HDS.

Does the HDS indicate FAILED?
-YES- Replace the WU-TWC Warm Up TWC Removal and Installation, then do the repair verification.
-NO- If the HDS indicates PASSED, intermittent failure, the system is OK at this time. If the HDS indicates EXECUTING, keep driving until a result comes on. If the HDS indicates OUT OF CONDITION, go to step 1-4 and recheck.

Repair verification (OBD STATUS check):

-1. Turn the ignition switch to ON (II).

-2. Reset the ECM with the HDS How To Troubleshoot The Fuel And Emissions Systems.

-3. Do the ECM idle learn procedure. ECM/PCM Idle Learn Procedure

-4. Drive the vehicle until the result of CAT MONITOR CONDITION in the DATA LIST on HDS indicates OK.
NOTE: Test-drive may to 10 minutes or more.

-5. Test-drive under these conditions:
* Engine coolant temperature (ECT SENSOR 1) above 158 °F (70 °C)
* Transmission in 5th
* Vehicle speed between 45-75 mph (72-120 km/h) for 5 minutes or more with cruise control set
* Vehicle speed between 55-75 mph (72-120 km/h) for 10 seconds, then decelerate (with the throttle fully closed). Repeat this three or more times
* Maintain the vehicle speed at 55 mph (88 km/h) for 5 minutes or more with cruise control set

-6. Monitor the OBD STATUS for DTC P0420 with the HDS.

Does the HDS indicate PASSED, FAILED, EXECUTING, or OUT OF CONDITION?
-PASSED- Troubleshooting is complete. If any other Pending or Confirmed DTCs were indicated, go to the indicated DTC's troubleshooting.
-FAILED- Go to step 1 and recheck.
-EXECUTING- Keep the test condition until a result comes on.
-OUT OF CONDITION- Meet the test condition, and check the OBD STATUS again.