DTC P0421, P0431 [AJ] (VIN: JM0 LW10J300 301406-, JMZ LW69J7*# 307683-, JM8 LW28J**# 301514-, JM8 LW28A**# 301514- (Assumed))

BME010200400W04

DTC P0421

DTC P0431

Warm-up catalyst system (RH/LH) efficiency below threshold

DETECTION CONDITION

• PCM compares the number of HO2S (Front) and HO2S (Rear) inversions for a predetermined time. PCM monitors the number of inversions the rear side performs while the front side inverts for a specified number of times when the following monitoring conditions are met. PCM detects the inversion ratio. If inversion ratio is below threshold, PCM determined that catalyst system has deteriorated.
MONITORING CONDITION
- Engine speed 1,250- 2,000 rpm
- Calculated load 22- 44%
- Calculated TWC temperature is 400 °C {752 °F}
Diagnostic support note
• This is an intermittent monitor. (CATALYST)
• The MIL illuminates if the PCM detects the above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM.
• PENDING CODE is available if the PCM detects the above malfunction condition during the first drive cycle.
• FREEZE FRAME DATA is available.
• DTC is stored in the PCM memory.

POSSIBLE CAUSE

• WU-TWC deterioration or malfunction
• Exhaust gas leakage
• Looseness of HO2S (Front)
• Looseness of HO2S (Rear)
• PCM malfunction

Diagnostic procedure

STEP

INSPECTION

ACTION

1
VERIFY FREEZE FRAME DATA AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED
• Have FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS (Catalyst related) been recorded?
Yes
Go to the next step.
No
Record FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS on repair order, then go to the next step.
2
VERIFY RELATED SERVICE INFORMATION AVAILABILITY
• Check for related Service Information availability.
• Is any related Service Information available?
Yes
Perform repair or diagnosis according to available Service Information.
• If vehicle is not repaired, go to next step.
No
Go to next step.
3
VERIFY RELATED PENDING CODE OR STORED DTCS
• Turn the ignition switch off then ON (Engine OFF).
• Verify related pending code or stored DTCs.
• Is other DTCs present?
Yes
Go to appropriate DTC troubleshooting.
No
Go to next step.
4
INSPECT EXHAUST SYSTEM FOR GAS LEAKAGE
• Visually inspect exhaust system for exhaust gas leakage.
• Is there any gas leakage?
Yes
Repair or replace faulty exhaust parts, then go to Step 7.
No
Go to next step.
5
INSPECT INSTALLATION OF FRONT AND REAR OXYGEN SENSORS
• Inspect for looseness of front and rear oxygen sensors.
• Is it normal?
Yes
Go to next step.
No
Retighten sensor, then go to Step 7.
6
INSPECT FRONT HO2S VOLTAGE
• Access O2S11 for P0421 or O2S21 for P0431 PID using WDS or equivalent.
• Verify PID while racing engine (in PARK or NEUTRAL).
• Is PID reading normal?

- Above 0.45 V when suddenly depress accelerator pedal (rich condition).

- Below 0.45 V just after release accelerator pedal (lean condition)

Yes
Replace WU-TWC, then go to next step.
No
Replace suspected sensor, then go to next step.
7
VERIFY TROUBLESHOOTING OF DTC P0421 OR P0431 COMPLETED
• Make sure to reconnect all disconnected connectors.
• Turn the ignition switch to ON (Engine OFF).
• Clear DTC from memory using WDS or equivalent.
• Run PCM adaptive memory procedure drive mode and HO2S heater, HO2S, and EGR system repair verification drive mode.
• Is PENDING CODE of same DTC present?
Yes
Replace PCM, then go to next step.
No
Go to next step.
8
VERIFY AFTER REPAIR PROCEDURE
• Perform "After Repair Procedure".
• Is there any DTC present?
Yes
Go to applicable DTC inspection.
No
Troubleshooting completed.