DTC P0420

DTC P0420	Catalyst system efficiency below threshold
DETECTION CONDITION	The PCM monitors the input voltage from the HO2S and the A/F sensor output current when the following conditions are met. If the input voltage change is extremely large compared to the output current change, the PCM determines that the catalyst system has deteriorated. MONITORING CONDITIONS ECT: more than 70°C {158°F} Catalyst converter temperature: more than 400°C {752°F} Engine speed: less than 5, 000 rpm LOAD: 20-50 % (maximum calculated toad value varies depending on engine speed) Time with purge control system does not operate: more than 20 s 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	Looseness of A/F sensor Leakage exhaust gas Purge control system malfunction VSS malfunction Eccentric shaft position sensor malfunction TWC malfunction ECT sensor malfunction PCM malfunction

Catalyst system efficiency below threshold

DETECTION CONDITION

The PCM monitors the input voltage from the HO2S and the A/F sensor output current when the following conditions are met. If the input voltage change is extremely large compared to the output current change, the PCM determines that the catalyst system has deteriorated.

MONITORING CONDITIONS

ECT: more than 70°C {158°F}
Catalyst converter temperature: more than 400°C {752°F}
Engine speed: less than 5, 000 rpm
LOAD: 20-50 % (maximum calculated toad value varies depending on engine speed)
Time with purge control system does not operate: more than 20 s

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

Looseness of A/F sensor
Leakage exhaust gas
Purge control system malfunction
VSS malfunction
Eccentric shaft position sensor malfunction
TWC malfunction
ECT sensor malfunction
PCM malfunction

DIAGNOSTIC PROCEDURE

STEP	INSPECTION		ACTION
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.
1		No	Record the FREEZE FRAME DATA (Mode 12) and DIAGNOSTIC MONITORING TEST RESULTS on the repair order, then go to the next step.
2	VERIFY RELATED REPAIR INFORMATION AVAILABILITY Verify related Service Bulletins and/or on-line repair information availability. Is any related repair information available?	Yes	Perform repair or diagnosis according to the available repair information. If the vehicle is not repaired, go to the next step.
2		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 the related PENDING CODE or stored DTCs. Are other DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE ).
3		No	Go to the next step.
4	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.
4		No	Retighten the A/F sensor, then go to Step 11. (See AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION ).
5	INSPECT EXHAUST SYSTEM FOR EXHAUST GAS LEAKAGE Visually inspect 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 11.
5		No	Go to the next step.
6	INSPECT PURGE CONTROL SYSTEM OPERATION Perform the Purge Control System Operation Inspection. (See ENGINE CONTROL SYSTEM OPERATION INSPECTION ). Does the purge control system operate properly?	Yes	Go to the next step.
6		No	Repair or replace the malfunctioning part according to the inspection results, then go to Step 11.
7	VERIFY CURRENT INPUT SIGNAL STATUS OF VSS Start the engine. Access the VSS PID using the M-MDS. (See ON-BOARD DIAGNOSTIC TEST ). Inspect the VSS PID. Is the PID normal? (See PCM INSPECTION ).	Yes	Go to the next step.
7		No	Repair or replace the malfunctioning part according to the inspection results, then go to Step 11.
8	INSPECT ECCENTRIC SHAFT POSITION SENSOR Inspect the eccentric shaft position sensor. (See ECCENTRIC SHAFT POSITION SENSOR INSPECTION ). Is there any malfunction?	Yes	Replace the eccentric shaft position sensor, then go to Step 11. (See ECCENTRIC SHAFT POSITION SENSOR REMOVAL/INSTALLATION ).
8		No	Go to the next step.
9	INSPECT TWC Inspect the TWC. (See THREE-WAY CATALYTIC CONVERTER (TWC) INSPECTION ). Is there any malfunction?	Yes	Replace the TWC, then go to Step 11. (See EXHAUST SYSTEM REMOVAL/INSTALLATION ).
9		No	Go to the next step.
10	INSPECT ECT SENSOR Inspect the ECT sensor. (See ENGINE COOLANT TEMPERATURE (ECT) SENSOR INSPECTION ). Is there any malfunction?	Yes	Replace the ECT sensor, then go to the next step. (See ENGINE COOLANT TEMPERATURE (ECT) SENSOR REMOVAL/INSTALLATION ).
10		No	Go to the next step.
11	VERIFY TROUBLESHOOTING OF DTC P0420 COMPLETED Make sure to reconnect all disconnected connectors. Clear the DTC from the PCM memory using the M-MDS. (See AFTER REPAIR PROCEDURE ). Perform the DRIVE MODE 3 (A/F sensor heater, HO2S heater, A/F sensor, HO2S, and TWC Repair Verification Drive Mode). (See OBD-II DRIVE MODE ). Is the PENDING CODE same as the DTC present?	Yes	Replace the PCM, then go to the next step. (See PCM REMOVAL/INSTALLATION ).
11		No	Go to the next step.
12	VERIFY AFTER REPAIR PROCEDURE Perform the "AFTER REPAIR PROCEDURE ". (See AFTER REPAIR PROCEDURE ). Are any DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE ).
12		No	DTC troubleshooting completed.