DTC P0421 [L8, LF]

id0102b1807300

DTC P0421 | Warm up catalyst system efficiency below threshold
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DETECTION CONDITION | • The PCM compares number of A/F sensor and HO2S inversions for a predetermined time. The PCM monitors number of inversions rear side performs while front side inverts for a specified number of times when the following monitoring conditions are met, the PCM detects inversion ratio. If inversion ratio is below threshold, the PCM determines that catalyst has deteriorated. MONITORING CONDITIONS ― Calculated TWC temperature: more than 400 °C {752 °F} ― Engine speed: 1,500—3,000 rpm (AT)/3,500 rpm (MT) ― LOAD: 15—48% (at engine speed 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. • FREEZE FRAME DATA (Mode 2/Mode 12) is available. • The DTC is stored in the PCM memory.
POSSIBLE CAUSE | • Exhaust gas leakage • A/F sensor looseness • HO2S looseness • TWC deterioration or malfunction • PCM malfunction

Diagnostic procedure

STEP | INSPECTION | ACTION
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1 | VERIFY FREEZE FRAME DATA (MODE 12) AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED • Have the FREEZE FRAME DATA (Mode 12) and DIAGNOSTIC MONITORING TEST RESULTS (catalyst related) been recorded? | Yes | Go to the next step.
No | Record the FREEZE FRAME DATA (Mode 12) and DIAGNOSTIC MONITORING TEST RESULTS on repair order, then go to the next step.
2 | VERIFY RELATED SERVICE 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 AND STORED DTC • Turn the ignition switch off, then to the ON position (engine off). • Perform the Pending Trouble Code Access Procedure and DTC Reading Procedure. (See ON-BOARD DIAGNOSTIC TEST [L8, LF].) • Are any DTCs present? | Yes | Go to the applicable DTC troubleshooting. (See DTC TABLE [L8, LF].)
No | Go to the next step.
4 | INSPECT EXHAUST SYSTEM FOR EXHAUST GAS LEAKAGE • Visually inspect the exhaust gas leakage in the exhaust system. • Is there exhaust gas leakage? | Yes | Repair or replace the malfunctioning part, then go to Step 8. (See EXHAUST SYSTEM REMOVAL/INSTALLATION [L8, LF].)
No | Go to the next step.
5 | INSPECT INSTALLATION OF A/F SENSOR • Inspect if the A/F sensor is loosely installed. • Is the A/F sensor installed securely? | Yes | Go to the next step.
No | Retighten the A/F sensor, then go to Step 8. (See AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION [L8, LF].)
6 | INSPECT INSTALLATION OF HO2S • Inspect if the HO2S is loosely installed. • Is the HO2S installed securely? | Yes | Go to the next step.
No | Retighten the HO2S, then go to Step 8. (See HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION [L8, LF].)
7 | INSPECT TWC • Clear the DTC from the PCM memory using the M-MDS. (See AFTER REPAIR PROCEDURE [L8, LF].) • Turn the ignition switch off then to the ON position. • Inspect the TWC. (See EXHAUST SYSTEM INSPECTION [L8, LF].) • Is there any malfunction? | Yes | Replace the TWC, then go to the next step. (See EXHAUST SYSTEM REMOVAL/INSTALLATION [L8, LF].)
No | Replace the A/F sensor and HO2S, then go to the next step. (See AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION [L8, LF].) (See HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION [L8, LF].)
8 | VERIFY DTC TROUBLESHOOTING COMPLETED • Make sure to reconnect all disconnected connectors. • Turn the ignition switch to the ON position (engine off). • Clear the DTC from the PCM memory using the M-MDS. (See AFTER REPAIR PROCEDURE [L8, LF].) • Perform the Drive Mode 03 (A/F sensor heater, HO2S heater, A/F sensor, HO2S and TWC Repair Verification). (See OBD DRIVE MODE [L8, LF].) • Is the PENDING CODE for this DTC present? | Yes | Replace the PCM, then go to the next step. (See PCM REMOVAL/INSTALLATION [L8, LF].)
No | Go to the next step.
9 | VERIFY AFTER REPAIR PROCEDURE • Perform the “AFTER REPAIR PROCEDURE”. (See AFTER REPAIR PROCEDURE [L8, LF].) • Are any DTCs present? | Yes | Go to the applicable DTC troubleshooting. (See DTC TABLE [L8, LF].)
No | DTC troubleshooting completed.