DTC P0421:00 [L5]

DTC P0421:00	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 counts when the following conditions are met. The PCM detects inversion ratio. If the inversion ratio is below specification, the PCM determine that the catalyst system has deteriorated. ― The A/F sensor inversion counts 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 CONDITIONS ― Catalyst converter temperature: more than 400 °C {752 °F} ― Engine speed: 1,200—3,000 rpm ― Charging efficiency: 15—48% (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 first drive cycle. • FREEZE FRAME DATA (Mode 2)/Snapshot data is available. • The DTC is stored in the PCM memory.
POSSIBLE CAUSE	• Leakage exhaust system • Looseness A/F sensor • Looseness HO2S • TWC malfunction • PCM malfunction

DTC P0421:00

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 counts when the following conditions are met. The PCM detects inversion ratio. If the inversion ratio is below specification, the PCM determine that the catalyst system has deteriorated.

― The A/F sensor inversion counts 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 CONDITIONS

― Catalyst converter temperature: more than 400 °C {752 °F}

― Engine speed: 1,200—3,000 rpm

― Charging efficiency: 15—48% (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 first drive cycle.

• FREEZE FRAME DATA (Mode 2)/Snapshot data is available.

• The DTC is stored in the PCM memory.

POSSIBLE CAUSE

• Leakage exhaust system

• Looseness A/F sensor

• Looseness HO2S

• TWC malfunction

• PCM malfunction

STEP	INSPECTION	ACTION
1	VERIFY FREEZE FRAME DATA (MODE 2)/SNAPSHOT DATA AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED • Have the FREEZE FRAME DATA (Mode 2)/snapshot data and DIAGNOSTIC MONITORING TEST RESULTS (catalyst related) been recorded?	Yes	Go to the next step.
No	Record the FREEZE FRAME DATA (Mode 2)/snapshot data and DIAGNOSTIC MONITORING TEST RESULTS on the 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/OR 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 [L5].) • Are any other PENDING CODEs and/or DTCs present?	Yes	Go to the applicable PENDING CODE or DTC inspection. (See DTC TABLE [L5].)
No	Go to the next step.
4	INSPECT GAS LEAKAGE FROM EXHAUST SYSTEM • Visually inspect the exhaust gas leakage in the exhaust system. • Is there any leakage?	Yes	Repair or replace the malfunctioning part according to the inspection results, then go to Step 8.
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 [L5].)
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 [L5].)
7	INSPECT TWC • Clear the DTC from the PCM memory using the M-MDS. (See AFTER REPAIR PROCEDURE [L5].) • Turn the ignition switch off, then to the ON position (engine off). • Inspect the TWC. (See EXHAUST SYSTEM INSPECTION [L5].) • Is there any malfunction?	Yes	Replace the TWC, then go to the next step. (See EXHAUST SYSTEM REMOVAL/INSTALLATION [L5].)
No	Go to the next step.
8	VERIFY DTC TROUBLESHOOTING COMPLETED • Make sure to reconnect all disconnected connectors. • Clear the DTC from the PCM memory using the M-MDS. (See AFTER REPAIR PROCEDURE [L5].) • Perform the Drive Mode 03 (EGR System, A/F sensor heater, HO2S heater, A/F sensor, HO2S and TWC Repair Verification Drive Mode). (See OBD DRIVE MODE [L5].) • Is the PENDING CODE for this DTC present?	Yes	Replace the PCM, then go to the next step. (See PCM REMOVAL/INSTALLATION [L5].)
No	Go to the next step.
9	VERIFY AFTER REPAIR PROCEDURE • Perform the “AFTER REPAIR PROCEDURE”. (See AFTER REPAIR PROCEDURE [L5].) • Are any DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE [L5].)
No	DTC troubleshooting completed.

STEP

INSPECTION

ACTION

VERIFY FREEZE FRAME DATA (MODE 2)/SNAPSHOT DATA AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED

• Have the FREEZE FRAME DATA (Mode 2)/snapshot data and DIAGNOSTIC MONITORING TEST RESULTS (catalyst related) been recorded?

Yes

Go to the next step.

Record the FREEZE FRAME DATA (Mode 2)/snapshot data and DIAGNOSTIC MONITORING TEST RESULTS on the repair order, then go to the next step.

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.

Go to the next step.

VERIFY RELATED PENDING CODE AND/OR 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 [L5].)

• Are any other PENDING CODEs and/or DTCs present?

Yes

Go to the applicable PENDING CODE or DTC inspection.

(See DTC TABLE [L5].)

Go to the next step.

INSPECT GAS LEAKAGE FROM EXHAUST SYSTEM

• Visually inspect the exhaust gas leakage in the exhaust system.

• Is there any leakage?

Yes

Repair or replace the malfunctioning part according to the inspection results, then go to Step 8.

Go to the next step.

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.

Retighten the A/F sensor, then go to Step 8.

(See AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION [L5].)

INSPECT INSTALLATION OF HO2S

• Inspect if the HO2S is loosely installed.

• Is the HO2S installed securely?

Yes

Go to the next step.

Retighten the HO2S, then go to Step 8.

(See HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION [L5].)

INSPECT TWC

• Clear the DTC from the PCM memory using the M-MDS. (See AFTER REPAIR PROCEDURE [L5].)

• Turn the ignition switch off, then to the ON position (engine off).

• Inspect the TWC. (See EXHAUST SYSTEM INSPECTION [L5].)

• Is there any malfunction?

Yes

Replace the TWC, then go to the next step.

(See EXHAUST SYSTEM REMOVAL/INSTALLATION [L5].)

Go to the next step.

VERIFY DTC TROUBLESHOOTING COMPLETED

• Make sure to reconnect all disconnected connectors.

• Clear the DTC from the PCM memory using the M-MDS. (See AFTER REPAIR PROCEDURE [L5].)

• Perform the Drive Mode 03 (EGR System, A/F sensor heater, HO2S heater, A/F sensor, HO2S and TWC Repair Verification Drive Mode). (See OBD DRIVE MODE [L5].)

• Is the PENDING CODE for this DTC present?

Yes

Replace the PCM, then go to the next step.

(See PCM REMOVAL/INSTALLATION [L5].)

Go to the next step.

VERIFY AFTER REPAIR PROCEDURE

• Perform the “AFTER REPAIR PROCEDURE”. (See AFTER REPAIR PROCEDURE [L5].)

• Are any DTCs present?

Yes

Go to the applicable DTC inspection.

(See DTC TABLE [L5].)

DTC troubleshooting completed.