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DTC P0421 [L3 Turbo]

id0102b7807300

DTC P0421 | Warm up catalyst system efficiency below threshold
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DETECTION CONDITION | • The PCM compares the number of A/F sensor and HO2S inversions for a predetermined time. The 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. The PCM detects the inversion ratio. If the inversion ratio is below the threshold, The PCM determines that the catalyst system has deteriorated. MONITORING CONDITIONS - Engine speed: 1,500- 3,000 rpm - Calculated TWC temperature: above 400 °C {752 °F} - LOAD: 15- 48% (at engine speed of 2,000 rpm) 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. • DIAGNOSTIC MONITORING TEST RESULTS is available. • FREEZE FRAME DATA is available. • The DTC is stored in the PCM memory.
POSSIBLE CAUSE | • TWC deterioration or malfunction • Exhaust gas leakage • Loose A/F sensor • Loose HO2S • PCM malfunction

Diagnostic procedure

STEP | INSPECTION | ACTION
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1 | VERIFY FREEZE FRAME DATA AND DIAGNOSTIC MONITORING TEST RESULTS HAS BEEN RECORDED • Has FREEZE FRAME DATA been recorded? | Yes | Go to the next step.
No | Record the FREEZE FRAME DATA on the repair order, then go to the next step.
2 | VERIFY RELATED REPAIR INFORMATION AVAILABILITY • Verify related Service Information availability. • Is any related Service Information available? | Yes | Perform repair or diagnosis according to the available Service information. If the vehicle is not repaired, go to the next step.
No | Go to the next step.
3 | VERIFY RELATED PENDING CODE OR STORED DTC • Turn the ignition switch off, then to the ON position (Engine off). • Verify the related PENDING CODE or stored DTCs. • Are other DTCs present? | Yes | Go to the applicable DTC inspection. (See DTC TABLE [L3 Turbo].)
No | Go to the next step.
4 | INSPECT EXHAUST SYSTEM FOR EXHAUST GAS LEAKAGE • Visually inspect for exhaust gas leakage in the exhaust system. • Is there exhaust gas leakage? | Yes | Repair or replace the malfunctioning part, then go to Step 7.
No | Go to the next step.
5 | INSPECT INSTALLATION OF A/F SENSOR AND HO2S • Inspect the A/F sensor and HO2S for looseness. • Is it normal? | Yes | Go to the next step.
No | Retighten the sensor, then go to Step 7. (See EXHAUST SYSTEM REMOVAL/INSTALLATION [L3 Turbo].)
6 | INSPECT TWC • Clear the DTC using the WDS or equivalent generic OBD function. • Turn the ignition switch off then back to the ON position. • Inspect the TWC. • Is it normal? | Yes | Replace the A/F sensor or HO2S, then go to the next step.
No | Replace the TWC, then go to the next step.
7 | 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 WDS or equivalent. • Perform the A/F sensor heater, HO2S heater, A/F sensor, HO2S, and TWC Repair Verification Drive Mode. (See OBD DRIVE MODE [L3 Turbo].) • Is the PENDING CODE for this DTC present? | Yes | Replace the PCM, then go to the next step. (See PCM REMOVAL/INSTALLATION [L3 Turbo].)
No | Go to the next step.
8 | VERIFY AFTER REPAIR PROCEDURE • Perform the "AFTER REPAIR PROCEDURE". (See AFTER REPAIR PROCEDURE [L3 Turbo].) • Are any DTCs present? | Yes | Go to the applicable DTC troubleshooting. (See DTC TABLE [L3 Turbo].)
No | Troubleshooting completed.