LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Acura >> 2012 >> TL Base >> Repair and Diagnosis >> Engine Performance >> System >> Catalytic Converter System >> DTC Troubleshooting >> DTC P0420: Rear Bank Catalyst System Efficiency Below Threshold (Bank 1); DTC P0430: Front Bank Catalyst System Efficiency Below Threshold (Bank 2)
April 5, 2026: LEMON Manuals is launched! Read the announcement.

DTC P0420: Rear Bank Catalyst System Efficiency Below Threshold (Bank 1); DTC P0430: Front Bank Catalyst System Efficiency Below Threshold (Bank 2)

NOTE:
  • Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information (see GENERAL TROUBLESHOOTING INFORMATION ).
  • If some of the DTCs listed below are stored at the same time as DTC P0420 and/or P0430*, troubleshoot those DTCs first, then recheck for DTC P0420 and/or P0430*.

    P0137, P0138, P0157*, P0158*: Secondary HO2S (Sensor 2)

    P0141, P0161*: Secondary HO2S (Sensor 2) heater

  • Poor quality fuel can cause these DTCs.
  • Information marked with an asterisk (*) applies to the front bank (Bank 2).
  1. Turn the ignition switch to ON (II), or press the engine start/stop button to select the ON mode.
  2. Clear the DTC with the HDS.
  3. Start the engine. Hold the engine speed at 3, 000 RPM without load (A/T in P or N, M/T 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)
    • A/Tin D, or M/T in 4th
    • 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 (88- 120 km/h) for 10 seconds, then decelerate (with the throttle fully closed). Repeat this 3 times or more
    • 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 and/or P0430* 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 and recheck.

  6. Continue test driving until a result comes on.
  7. Monitor the OBD STATUS for DTC P0420 and/or P0430* 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), or press the engine start/stop button to select the ON mode.
  9. Replace the WU-TWC:
    • For DTC P0420, replace the rear WU-TWC (Bank 1) (see REAR (Bank 1)  ).
    • For DTC P0430, replace the front WU-TWC (Bank 2) (see FRONT (Bank 2)  ).
  10. Turn the ignition switch to ON (II), or press the engine start/stop button to select the ON mode.
  11. Reset the ECM/PCM with the HDS.
  12. Do the ECM/PCM idle learn procedure (see ECM/PCM IDLE LEARN PROCEDURE ).
  13. Test-drive for about 10 minutes, continually changing the vehicle speed.
  14. Check the CATA MONITOR CONDITION B1 (B2)* 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)
    • A/Tin D, or M/T in 4th
    • Vehicle speed between 55- 75 mph (88 - 120 km/h) for 10 seconds, then decelerate (with the throttle fully closed). Repeat this 3 times or more
    • Maintain the vehicle speed at 55 mph (88 km/h) for 5 minutes or more with cruise control set
  16. Continue test driving until a result comes on.
  17. Check for Pending or Confirmed DTCs with the HDS.

    Is DTC P0420 and/or P0430* indicated? 

    YES  - Check the fuel quality, then go to step  1.

    NO  - Go to step 18.

  18. Monitor the OBD STATUS for DTC P0420 and/or P0430* in the DTCs MENU with the HDS.

    Does the screen indicate PASSED? 

    YES  - Troubleshooting is complete. If any other Pending or Confirmed DTCs were indicated in step  17, go to the indicated DTC'S TROUBLESHOOTING .

    NO  - If the screen indicates FAILED, check the fuel quality, then go to step  1. If the screen indicates EXECUTING, keep driving until a result comes on. If the screen indicates OUT OF CONDITION, go to step  15.

scientia non olet · About LEMON Manuals