Intention of troubleshooting procedure

WARNING: This page is about a different variant/trim than selected.

Step 1-2
- Perform inspection of HO2S and A/F sensor signal related parts.
Step 3-7
- Perform inspection of each separate part.
Repair completion verification
- Verify that the primary malfunction is resolved and there are no other malfunctions.

P0421: 00 (PCM (PYUL)) DIAGNOSTIC PROCEDURE

Step	Inspection	Results	Action
1	PURPOSE: VERIFY HO2S IS INSTALLED POORLY Verify the HO2S installation condition. (Refer to [HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION ] ). Is the installation condition normal?	Yes	Go to the next step.
1		No	Correctly install the HO2S and perform the repair completion verification 1. (Refer to [HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION ] ).
2	PURPOSE: VERIFY A/F SENSOR IS INSTALLED POORLY Verify the A/F sensor installation condition. (Refer to [AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION ] ). Is the installation condition normal?	Yes	Replace the A/F sensor and/or HO2S and perform the repair completion verification 1. (Refer to [AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION ] ). (Refer to [HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION ] ).
2		No	Correctly install the A/F sensor and perform the repair completion verification 1. (Refer to [AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION ] ).
3	PURPOSE: VERIFY HO2S IS INSTALLED POORLY Verify the HO2S installation condition. (Refer to [HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION ] ). Is the installation condition normal?	Yes	Go to the next step.
3		No	Correctly install the HO2S and perform the repair completion verification 1. (Refer to [HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION ] ).
4	PURPOSE: VERIFY A/F SENSOR IS INSTALLED POORLY Verify the A/F sensor installation condition. (Refer to [AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION ] ). Is the installation condition normal?	Yes	Go to the next step.
4		No	Correctly install the A/F sensor and perform the repair completion verification 1. (Refer to [AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION ] ).
5	PURPOSE: INSPECT FOR EXHAUST GAS LEAKAGE FROM EXHAUST SYSTEM Visually inspect for exhaust gas leakage from exhaust system. Is there any malfunction?	Yes	Repair or replace the malfunctioning location and perform the repair completion verification 1.
5		No	Go to the next step.
6	PURPOSE: VERIFY IF OTHER DTCs OCCURRED SIMULTANOUSLY Install/connect the part removed/disconnected during the troubleshooting procedure. Clear the DTC recorded in the memory. (See CLEARING DTC .) Implement the repeatability verification procedure. (See Repeatability Verification Procedure ). Perform the DTC inspection for the PCM. (See DTC INSPECTION .) Are any other DTCs displayed?	Yes	Repair or replace the malfunctioning location according to the applicable DTC troubleshooting. (See DTC TABLE [PCM (PYUL)] ). Go to the next step.
6		No	Go to the next step.
7	VERIFY IF MALFUNCTION CAUSED BY CATALYTIC CONVERTER (WU-TWC) MALFUNCTION Clear the DTC recorded in the memory. (See CLEARING DTC .) Implement the repeatability verification procedure. (See Repeatability Verification Procedure ). Perform the DTC inspection for the PCM. (See DTC INSPECTION .) Is the same Pending DTC present?	Yes	Replace the exhaust manifold and perform the repair completion verification 1. (Refer to [CATALYTIC CONVERTER (GPF) REMOVAL/INSTALLATION ] ).
7		No	DTC troubleshooting completed.
Repair completion verification 1	PURPOSE: VERIFY THAT VEHICLE IS REPAIRED Install/connect the part removed/disconnected during the troubleshooting procedure. Clear the DTC recorded in the memory. (See CLEARING DTC .) Replicate the vehicle conditions at the time the DTC was detected using the following procedure. Implement the repeatability verification procedure. (See Repeatability Verification Procedure ). Perform the DTC inspection for the PCM. (See DTC INSPECTION .) Is the same Pending DTC present?	Yes	Refer to the controller area network (CAN) malfunction diagnosis flow to inspect for a CAN communication error. (See MALFUNCTION DIAGNOSIS FLOW [CONTROLLER AREA NETWORK (CAN)] .) If the CAN communication is normal, perform the diagnosis from Step 1. If the malfunction recurs, replace the PCM, then go to the next step. (Refer to [PCM REMOVAL/INSTALLATION ] ).
Repair completion verification 1		No	Go to the next step.
Repair completion verification 2	PURPOSE: VERIFY IF OTHER DTCs DISPLAYED Perform the DTC inspection. (See DTC INSPECTION .) Are any other DTCs displayed?	Yes	Repair or replace the malfunctioning location according to the applicable DTC troubleshooting.
Repair completion verification 2		No	DTC troubleshooting completed.