DTC Troubleshooting

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 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
- Poor quality fuel can cause these 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 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 (72-120 km/h) for 5 minutes or more with cruise control set
- '09-11 models: Vehicle speed between 55-75 mph (88-120 km/h) for 10 seconds, then decelerate (with throttle fully closed). Repeat this three or more times
- '06 and '09-11 models: Maintain the vehicle speed at 55 mph (88 km/h) for 5 minutes or more with cruise control set
'07-08 models: Maintain the vehicle speed at 55 mph (88 km/h) for 30 seconds or more

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

Does the screen indicate EXECUTING?

YES -

Go to step 6.

NO -

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

YES -

Go to step 8.

NO -

If the screen indicates PASSED, intermittent failure, the system is OK at this time. If the screen indicates EXECUTING, keep driving until a result comes on. If the screen indicates OUT OF CONDITION, go to step 4 and recheck.

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

9. Replace the TWC Service and Repair.

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

11. Reset the ECM with the HDS.

12. Do the ECM idle learn procedure ECM/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 condition 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)
- '09-11 models: Vehicle speed between 55-75 mph (88-120 km/h) for 10 seconds, then decelerate (with throttle fully closed). Repeat this three or more times
- '06 and '09-11 models: Vehicle speed at 55 mph (88 km/h) for 5 minutes
'07-08 models: Vehicle speed at 55 mph (88 km/h) for 30 seconds or more

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

Does the screen 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 -

Check the fuel quality, then go to step 1.

NO -

Go to step 19.

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

Does the screen indicate PASSED?

YES -

Troubleshooting is complete. If any other Pending or Confirmed DTCs wear indicated in step 18, go to the indicated DTC's troubleshooting.�

NO -

If the screen indicates FAILED, check for poor connections or loose terminal at secondary HO2S (Sensor 2) and the ECM. If the screen indicates EXECUTING, keep driving until a result comes on. If the screen indicates OUT OF CONDITION, go to step 13.