DTC P0421:00 [L3 Turbo]

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 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 CONDITIONS ― Engine speed: 1,300—2,850 rpm ― Calculated TWC temperature: above 400 °C {752 °F} ― Absolute load: 15—70% (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. • FREEZE FRAME DATA (Mode 2)/Snapshot data is available. • The DTC is stored in the PCM memory.
POSSIBLE CAUSE	• Exhaust gas leakage • Loose A/F sensor • Loose HO2S • TWC deterioration or 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 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 CONDITIONS

― Engine speed: 1,300—2,850 rpm

― Calculated TWC temperature: above 400 °C {752 °F}

― Absolute load: 15—70% (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.

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

• The DTC is stored in the PCM memory.

POSSIBLE CAUSE

• Exhaust gas leakage

• Loose A/F sensor

• Loose HO2S

• TWC deterioration or 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 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 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 DTC Reading Procedure and Pending Trouble Code Access Procedure. (See ON-BOARD DIAGNOSTIC TEST [L3 Turbo].) • Are any other DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE [L3 Turbo].)
No	Go to the next step.
4	INSPECT EXHAUST GAS LEAKAGE • Visually inspect for the exhaust gas leakage in the exhaust system. • Is there exhaust gas 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 [L3 Turbo].)
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 [L3 Turbo].)
7	INSPECT TWC • Clear the DTC from the PCM memory using the M-MDS. (See AFTER REPAIR PROCEDURE [L3 Turbo].) • Turn the ignition switch off, then to the ON position (engine off). • Inspect the TWC. (See EXHAUST SYSTEM INSPECTION [L3 Turbo].) • Is there any malfunction?	Yes	Replace the TWC, then go to the next step. (See EXHAUST SYSTEM REMOVAL/INSTALLATION [L3 Turbo].)
No	Replace the HO2S, then go to the next step. (See HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION [L3 Turbo].)
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 [L3 Turbo].) • 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 [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.
9	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 inspection. (See DTC TABLE [L3 Turbo].)
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 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 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 STORED DTC

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

• Perform the DTC Reading Procedure and Pending Trouble Code Access Procedure. (See ON-BOARD DIAGNOSTIC TEST [L3 Turbo].)

• Are any other DTCs present?

Yes

Go to the applicable DTC inspection.

(See DTC TABLE [L3 Turbo].)

Go to the next step.

INSPECT EXHAUST GAS LEAKAGE

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

• Is there exhaust gas 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 [L3 Turbo].)

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 [L3 Turbo].)

INSPECT TWC

• Clear the DTC from the PCM memory using the M-MDS. (See AFTER REPAIR PROCEDURE [L3 Turbo].)

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

• Inspect the TWC. (See EXHAUST SYSTEM INSPECTION [L3 Turbo].)

• Is there any malfunction?

Yes

Replace the TWC, then go to the next step.

(See EXHAUST SYSTEM REMOVAL/INSTALLATION [L3 Turbo].)

Replace the HO2S, then go to the next step.

(See HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION [L3 Turbo].)

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 [L3 Turbo].)

• 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 [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].)

Go to the next step.

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 inspection.

(See DTC TABLE [L3 Turbo].)

DTC troubleshooting completed.