DTC P0420:00 [ZJ, ZY]

DTC P0420:00	Catalyst system efficiency below threshold
DETECTION CONDITION	• The PCM compares the number of the 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 inversion ratio is below the threshold, the PCM determines that the catalyst system has deteriorated. MONITORING CONDITIONS ― A/F Sensor Heater, HO2S Heater, A/F Sensor, HO2S, and TWC Repair Verification Drive Mode ― Engine speed: 1,500— 3,000 rpm ― Calculated TWC temperature in PCM: more than 540 °C {1,004 °F} ― Absolute load: 17—48%^1 ^1: Maximum absolute load value varies depending on the engine speed. Diagnostic support note • This is a 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 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 • A/F sensor malfunction • HO2S malfunction • PCM malfunction

DTC P0420:00

Catalyst system efficiency below threshold

DETECTION CONDITION

• The PCM compares the number of the 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 inversion ratio is below the threshold, the PCM determines that the catalyst system has deteriorated.

MONITORING CONDITIONS

― A/F Sensor Heater, HO2S Heater, A/F Sensor, HO2S, and TWC Repair Verification Drive Mode

― Engine speed: 1,500— 3,000 rpm

― Calculated TWC temperature in PCM: more than 540 °C {1,004 °F}

― Absolute load: 17—48%^*1

^*1: Maximum absolute load value varies depending on the engine speed.

Diagnostic support note

• This is a 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 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

• A/F sensor malfunction

• HO2S malfunction

• PCM malfunction

STEP	INSPECTION	ACTION
1	VERIFY FREEZE FRAME DATA AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED • Have the FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS (catalyst related) been recorded?	Yes	Go to the next step.
No	Record the FREEZE FRAME 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 STORED DTC • Turn the ignition switch off, then to the ON position (engine off). • Verify the related PENDING CODE and stored DTCs using the M-MDS. (See ON-BOARD DIAGNOSTIC TEST [ZJ, ZY].) • Are any other DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE [ZJ, ZY].)
No	Go to the next step.
4	INSPECT GAS LEAKAGE OF EXHAUST SYSTEM • Visually inspect the exhaust gas leakage in exhaust system. • Is there 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 [ZJ, ZY].)
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 [ZJ, ZY].)
7	INSPECT TWC • Clear the DTC from the PCM memory using the M-MDS. (See AFTER REPAIR PROCEDURE [ZJ, ZY].) • Turn the ignition switch off, then to the ON position. • Inspect the TWC. (See EXHAUST SYSTEM INSPECTION [ZJ, ZY].) • Is there any malfunction?	Yes	Replace the TWC, then go to the next step. (See EXHAUST SYSTEM REMOVAL/INSTALLATION [ZJ, ZY].)
No	Replace the A/F sensor and HO2S, then go to the next step. (See AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION [ZJ, ZY].) (See HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION [ZJ, ZY].)
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 [ZJ, ZY].) • Perform the Drive Mode 02 (A/F Sensor Heater, HO2S Heater, A/F Sensor, HO2S, and TWC Repair Verification Drive Mode). (See OBD DRIVE MODE [ZJ, ZY].) • Is the PENDING CODE for this DTC present?	Yes	Replace the PCM, then go to the next step. (See PCM REMOVAL/INSTALLATION [ZJ, ZY].)
No	Go to the next step.
9	VERIFY AFTER REPAIR PROCEDURE • Perform the “AFTER REPAIR PROCEDURE”. (See AFTER REPAIR PROCEDURE [ZJ, ZY].) • Are any DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE [ZJ, ZY].)
No	DTC troubleshooting completed.

STEP

INSPECTION

ACTION

VERIFY FREEZE FRAME DATA AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED

• Have the FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS (catalyst related) been recorded?

Yes

Go to the next step.

Record the FREEZE FRAME 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 STORED DTC

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

• Verify the related PENDING CODE and stored DTCs using the M-MDS.

(See ON-BOARD DIAGNOSTIC TEST [ZJ, ZY].)

• Are any other DTCs present?

Yes

Go to the applicable DTC inspection.

(See DTC TABLE [ZJ, ZY].)

Go to the next step.

INSPECT GAS LEAKAGE OF EXHAUST SYSTEM

• Visually inspect the exhaust gas leakage in exhaust system.

• Is there 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 [ZJ, ZY].)

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 [ZJ, ZY].)

INSPECT TWC

• Clear the DTC from the PCM memory using the M-MDS.

(See AFTER REPAIR PROCEDURE [ZJ, ZY].)

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

• Inspect the TWC.

(See EXHAUST SYSTEM INSPECTION [ZJ, ZY].)

• Is there any malfunction?

Yes

Replace the TWC, then go to the next step.

(See EXHAUST SYSTEM REMOVAL/INSTALLATION [ZJ, ZY].)

Replace the A/F sensor and HO2S, then go to the next step.

(See AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION [ZJ, ZY].)

(See HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION [ZJ, ZY].)

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 [ZJ, ZY].)

• Perform the Drive Mode 02 (A/F Sensor Heater, HO2S Heater, A/F Sensor, HO2S, and TWC Repair Verification Drive Mode).

(See OBD DRIVE MODE [ZJ, ZY].)

• Is the PENDING CODE for this DTC present?

Yes

Replace the PCM, then go to the next step.

(See PCM REMOVAL/INSTALLATION [ZJ, ZY].)

Go to the next step.

VERIFY AFTER REPAIR PROCEDURE

• Perform the “AFTER REPAIR PROCEDURE”.

(See AFTER REPAIR PROCEDURE [ZJ, ZY].)

• Are any DTCs present?

Yes

Go to the applicable DTC inspection.

(See DTC TABLE [ZJ, ZY].)

DTC troubleshooting completed.