DTC Troubleshooting

DTC Troubleshooting: P0420 (67)

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 Initial Inspection and Diagnostic Overview.
- 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-P0304: No. 1, No. 2, No. 3, or No. 4 cylinder misfire detected
- Poor quality fuel may cause this DTC.

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 P or N) 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 D
- Vehicle speed between 45-75 mph (72-120 km/h) for 5 minutes or more with cruise control set
- 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 in the DTCs MENU with the HDS.

Does the HDS indicate EXECUTING?

YES -

Go to step 6.

NO -

If the HDS indicates OUT OF CONDITION, go to step 4 and recheck. If the HDS indicates PASSED, intermittent failure, the system is OK at this time. If the HDS indicates FAILED, go to step 8.

6. Continue test driving until a result comes on.

7. Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the HDS.

Does the HDS indicate FAILED?

YES -

Go to step 8.

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 4 and recheck.

8. Turn the ignition switch to LOCK (0).

9. Replace the WU-TWC Warm Up TWC Removal/Installation.

10. Turn the ignition switch to ON (II).

11. Reset the PCM with the HDS.

12. Do the PCM idle learn procedure PCM Idle Learn Procedure.

13. Test-drive for about 10 minutes, continually changing the vehicle speed.

14. Check the CATA MONITOR CONDITION in the DATA LIST with the HDS.

Is the temperature OK?

YES -

Go to step 15.

NO -

Go to step 13 and recheck.

15. Test-drive under these conditions:

- Engine coolant temperature (ECT SENSOR 1) above 158 °F (70 °C)
- Transmission in D
- Vehicle speed at 55 mph (88 km/h) for 5 minutes or more with cruise control set

16. Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the HDS.

Does the HDS indicate EXECUTING?

YES -

Go to step 17.

NO -

Go to step 15 and recheck.

17. Continue test-driving until a result comes on.

18. Check for Pending or Confirmed DTCs with the HDS.

Is DTC P0420 indicated?

YES -

Go to the indicated DTC's troubleshooting.

NO -

Go to step 19.

19. Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the HDS.

Does the HDS indicate PASSED?

YES -

Troubleshooting is complete.

NO -

If the HDS indicates FAILED, check the fuel quality. If the HDS indicates EXECUTING, keep driving until a result comes on. If the HDS indicates OUT OF CONDITION, go to step 13.