Diagnostic procedure

DTC P0421 [L3] DIAGNOSTIC PROCEDURE

STEP	INSPECTION		ACTION
1	IDENTIFY TRIGGER DTC FOR FREEZE FRAME DATA (MODE 2) Is DTC P0421 on FREEZE FRAME DATA (Mode 2)?	Yes	Go to the next step.
1		No	Go to troubleshooting for DTC on FREEZE FRAME DATA (Mode 2). (See DTC TABLE .)
2	VERIFY FREEZE FRAME DATA (MODE 12) AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED Have FREEZE FRAME DATA (Mode 12) and DIAGNOSTIC MONITORING TEST RESULTS (Catalyst related) been recorded?	Yes	Go to the next step.
2		No	Record the FREEZE FRAME DATA (Mode 12) and DIAGNOSTIC MONITORING TEST RESULTS on repair order, then go to the next step.
3	VERIFY RELATED REPAIR INFORMATION AVAILABILITY Verify related Service Bulletins and/or on-line repair information availability. Is any related repair information available?	Yes	Perform repair or diagnosis according to available repair information. If vehicle is not repaired, go to the next step.
3		No	Go to the next step.
4	VERIFY RELATED PENDING CODE OR STORED DTC Turn the ignition switch off then to the ON position (Engine off). Verify related pending code or stored DTCs. Are other DTCs present?	Yes	Go to appropriate DTC troubleshooting.
4		No	Go to the next step.
5	INSPECT GAS LEAKAGE OF EXHAUST SYSTEM Visually inspect exhaust gas leakage in the exhaust system. Is there gas leakage?	Yes	Repair or replace the malfunctioning exhaust part, then go to Step 8.
5		No	Go to the next step.
6	INSPECT INSTALLATION OF A/F SENSOR AND HO2S Inspect for looseness of A/F sensor and HO2S. Is it normal?	Yes	Go to the next step.
6		No	Retighten the A/F sensor and/or HO2S, then go to Step 8.
7	INSPECT TWC Clear the DTC using the M-MDS generic OBD function. Turn the ignition switch off then back to the ON position. Inspect the TWC. (See WARM-UP THREE-WAY CATALYTIC CONVERTER (WU-TWC) INSPECTION .) Is it normal?	Yes	Replace the HO2S, then go to the next step.
7		No	Replace the TWC, then go to the next step.
8	VERIFY TROUBLESHOOTING OF DTC P0421 COMPLETED Make sure to reconnect all disconnected connectors. Turn the ignition switch to the ON position (Engine off). Clear the DTC from the memory using the M-MDS. Perform the A/F sensor heater, HO2S heater, A/F sensor, HO2S, and TWC Repair Verification Drive Mode. (See OBD-II DRIVE MODE .) Is the PENDING CODE for this DTC present?	Yes	Replace the PCM, then go to the next step. (See PCM REMOVAL/INSTALLATION .)
8		No	Go to the next step.
9	VERIFY AFTER REPAIR PROCEDURE Perform the "AFTER REPAIR PROCEDURE". (See AFTER REPAIR PROCEDURE .) Are any DTC present?	Yes	Go to the applicable DTC troubleshooting. (See DTC TABLE .)
9		No	Troubleshooting completed.