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*, P2270, P2272*: Secondary HO2S (Sensor 2)

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

P0300: Random misfire detected

P0301-P0306: No. 1, No. 2, No. 3, No. 4, No. 5, or No. 6 cylinder misfire detected

Poor quality fuel can cause these DTCs.
Information marked with an asterisk (*) applies to the front bank (Bank 2).

Turn the ignition switch to ON (II), or press the engine start/stop button to select the ON mode.
Clear the DTC with the HDS.
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.
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
- Vehicle speed between 55-75 mph (88-120 km/h) for 10 seconds, then decelerate (with the throttle fully closed). Repeat this three or more times.
- Maintain the vehicle speed at 55 mph (88 km/h) for 5 minutes or more with cruise control set
Monitor the OBD STATUS for DTC P0420 and/or P0430* 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.
Continue test driving until a result comes on.
Monitor the OBD STATUS for DTC P0420 and/or P0430, 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.
Turn the ignition switch to LOCK (0), or press the engine start/stop button to select the OFF mode.
Replace the WU-TWC:
- For DTC P0420, replace the rear WU-TWC (Bank 1) (see REAR WU-TWC (Bank 1) ).
- For DTC P0430, replace the front WU-TWC (Bank 2) (see FRONT WU-TWC (Bank 2) ).
Turn the ignition switch to ON (II), or press the engine start/stop button to select the ON mode.
Reset the PCM with the HDS.
Do the PCM idle learn procedure (see PCM IDLE LEARN PROCEDURE ).
Test-drive for about 10 minutes, continually changing the vehicle speed.
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.
Test-drive under these conditions:
- Engine coolant temperature (ECT SENSOR 1) above 158°F(70°C)
- Transmission in D
- Vehicle speed between 55-75 mph (88-120 km/h) for 10 seconds, then decelerate (with the throttle fully closed). Repeat this three or more times.
- Maintain the vehicle speed at 55 mph (88 km/h) for 5 minutes or more with cruise control set.
Continue test driving until a result comes on.
Check for Pending or Confirmed DTCs with the HDS.
Is DTC P0420 and/or P0430* indicated?

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

NO -Go to step 18.
Monitor the OBD STATUS for DTC P0420 and/or P0430* in the DTCs MENU with the HDS.
Does the HDS indicate PASSED?

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

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