## DTC Troubleshooting: P0420 (67)

DTC P0420: | Catalyst System Efficiency Below Threshold

NOTE:

- If some of the DTCs listed below are stored ar the same time as DTC P0420, troubleshoot those DTCs first, then recheck for DTC P0420.
  P0137, P0138, P0140: Secondary HO2S (Sensor 2)
  P0141: Secondary HO2S (Sensor 2) Heater
- When poor quality FUEL is used, this DTC may indicate.

1. | Turn the ignition switch ON (II).

2. | Do the DTC CLEAR in the CLEAR MENU with the HDS.

3. | Start the engine. Hold the engine speed at 3,000 rpm (min-1) with no load (in neutral) until the radiator fan comes on, then let it idle.

4. | Test-drive for about 10 minutes. Then it drives, changing the vehicle speed.

5. | Check the CATA MON TEMP in the DATA LIST with the HDS. Is it OK? YES - Go to 6. NO - Go to 3 and recheck.

6. | Test-drive under following conditions. Engine Coolant temperature more than 70°C (158°F) Transmission in 5th gear Vehicle speed between 70 km/h (44 mph) and 80 km/h (50 mph)

7. | Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the HDS. Is it EXECUTING? YES - Go to 8. NO - Go to 6 and recheck.

8. | Test-drive continued untill a result comes on.

9. | Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the HDS. Is it FAILED? YES - Go to 10. NO - If it is PASSED, intermittent failure, system is OK at this time. If it is EXECUTING, keep the driving condition continually untill a result comes on. If it is Out of CONDITION, go to 6 and recheck.

10. | Turn the ignition switch OFF.

11. | Replace the TWC.

12. | Turn the ignition switch ON (II).

13. | Do the ECM RESET in the CLEAR MENU with the HDS.

14. | Do the ETCS learn procedure.

15. | Start the engine. Hold the engine speed at 3,000 rpm (min-1) with no load (in neutral) untill the radiator fan comes on, then let it idle.

16. | Test-drive for about 10 minutes. Then it drives, changing the vehicle speed.

17. | Check the CATA MON TEMP in the DATA LIST with the HDS. Is it OK? YES - Go to 18. NO - Go to 15 and recheck.

18. | Test-drive under following conditions. Engine Coolant temperature more than 70°C (158°F) Transmission in 5th gear Vehicle speed between 70 km/h (44 mph) and 80 km/h (50 mph)

19. | Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the HDS. Is it EXECUTING? YES - Go to 20. NO - Go to 18 and recheck.

20. | Test-drive continued untill a result comes on.

21. | Check for Temporary DTCs or DTCs in the DTCs MENU with the HDS. Are any Temporary DTCs or DTCs indicated? YES - Go to the indicated DTC troubleshooting.n NO - Go to 22.

22. | Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the HDS. Is it PASSED? YES - Troubleshooting is complete.n NO - If it is FAILED, check the fuel quality. If it is EXECUTING, keep the driving condition continually untill a result comes on. If it is Out of CONDITION, go to 18 and recheck.