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DTC P0420: Catalyst System Efficiency Below Threshold

NOTE:
  • Before you troubleshoot, record all freeze data and any on-board snapshot, and review GENERAL TROUBLESHOOTING INFORMATION .
  • If some of the DTCs listed below are stored at the same time as DTC P0420, troubleshoot them first, then recheck for DTC P0420.
  • Poor quality fuel may cause this DTC.
  1. Turn the ignition switch 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 gear
    • Vehicle speed between 45-75 mph (72-120 km/h) for 5 minutes or more
    • Vehicle speed 25 mph (40 km/h) or more for 1 minute with cruise control set
  5. Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the HDS.

    Does the screen indicate EXECUTING? 

    1. YES  - Go to step  6.
    2. 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? 

    1. YES  - Go to step  8.
    2. NO  - If the screen indicates PASSED, intermittent failure, 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 (O).
  9. Replace the three way catalytic converter (TWC) (see EXHAUST PIPE AND MUFFLER REPLACEMENT ).
  10. Turn the ignition switch ON (II).
  11. Reset the ECM with the HDS.
  12. Do ECM IDLE LEARN PROCEDURE .
  13. 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.
  14. Test-drive for about 10 minutes, varying the vehicle speed.
  15. Check the CAT MONITOR CONDITION in the DATA LIST with the HDS.

    Is the temperature OK? 

    1. YES  - Go to step  16.
    2. NO  - Go to step  13 and recheck.
  16. Test-drive under these conditions:
    • ECT SENSOR above 158°F (70°C)
    • Transmission in 5th gear
    • Vehicle speed between 45-75 mph (72-120 km/h) for 5 minutes or more
    • Vehicle speed 25 mph (40 km/h) or more for 5 minutes with cruise control set
  17. Check for Temporary DTCs or DTCs with the HDS

    Is DTC P0420 indicated? 

    1. YES  - Check the fuel quality, then go to step  1.
    2. NO  - Go to step  18.
  18. Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the HDS.

    Does the screen indicate PASSED? 

    1. YES  - Troubleshooting is complete. If any other Temporary DTCs or DTCS were indicated in step 17, go to the indicated DTC's troubleshooting. ■
    2. NO  - If the screen indicates FAILED, check for poor connections or loose terminals at the 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.
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