DTC P0421 [MTX, LF ATX (FS5A-EL)]

id0102b4807300

DTC P0421

Warm up catalyst system efficiency below threshold
DETECTION CONDITION
•  The PCM compares the number of A/F sensor and HO2S inversions for a predetermined time. The PCM monitors the HO2S inversion ratio when the following conditions are met: The PCM detects inversion ratio. If the inversion ratio is below threshold, the PCM determine that catalyst system has deteriorated.
―  The A/F sensor inversion ratio is as prescribed when the following monitoring conditions are met:
―  The accumulated occurrence time of the following monitoring conditions has exceeded the prescribed time limit:
MONITORING CONDITION
―  Engine speed is 1,600—3,000 rpm.
―  Calculated TWC temperature is above 400 °C {752 °F}.
―  Calculated load is 15—48% (at engine speed 2,000 rpm)
Diagnostic support note
•  This is a intermittent monitor. (Catalyst)
•  The MIL illuminates if the PCM detects the above malfunction conditions 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 PCM detects the above malfunction condition during 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
1
VERIFY FREEZE FRAME DATA HAVE BEEN RECORDED
•  Have FREEZE FRAME DATA been recorded?
Yes
Go to the next step.
No
Record the FREEZE FRAME DATA 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 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.
No
Go to the next step.
4
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 7.
No
Go to the next step.
5
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.
No
Retighten the sensor, then go to Step 7.
6
INSPECT A/F SENSOR
•  Inspect A/F sensor.
•  Is the A/F sensor normal?
Yes
Go to the next step.
No
Replace the A/F sensor, then go to Step 8.
(See AIR FUEL RATIO (A/F) SENSOR, HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION [LF, L3].)
7
INSPECT HO2S
•  Inspect HO2S.
•  Is the HO2S normal?
Yes
Replace the TWC, then go to the next step.
(See AIR FUEL RATIO (A/F) SENSOR, HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION [LF, L3].)
No
Replace the HO2S, 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.
•  Is the PENDING CODE for this DTC present?
Yes
Replace the PCM, then go to the next step.
(See PCM REMOVAL/INSTALLATION [LF, L3].)
No
Go to the next step.
9
VERIFY AFTER REPAIR PROCEDURE
•  Perform the “AFTER REPAIR PROCEDURE”.
•  Are any DTCs present?
Yes
Go to the applicable DTC troubleshooting.
(See DTC TABLE [MTX, LF ATX (FS5A-EL)].)
No
Troubleshooting completed.