DTC P0420


DTC P0420	Catalyst system efficiency below threshold
DETECTION CONDITION	• The PCM monitors the input voltage from the rear HO2S and the front HO2S 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 CONDITION - ECT: more than 70 °C {158 °F} - Catalyst converter temperature: more than 400 °C {752 °F} - Engine speed: 1,500- 3,500 rpm - LOAD: 20- 50% (maximum calculated load 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 is available. • The DTC is stored in the PCM memory.
POSSIBLE CAUSE	• Looseness of front HO2S • Leakage exhaust gas • Purge control system malfunction • VSS malfunction • ECT malfunction • Eccentric shaft position sensor malfunction • Catalytic converter malfunction • PCM malfunction


STEP	INSPECTION		ACTION
1	VERIFY FREEZE FRAME DATA HAS BEEN RECORDED • Has FREEZE FRAME DATA been recorded?	Yes	Go to the next step.
1		No	Record the FREEZE FRAME DATA on the repair order, then go to the next step.
2	VERIFY RELATED REPAIR INFORMATION AVAILABILITY • Verify related service 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 FRONT HO2S • Inspect the front HO2S for looseness. • Is it normal?	Yes	Go to the next step.
4		No	Tighten the front HO2S, then go to Step 11. (See FRONT HEATED OXYGEN SENSOR (HO2S) 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, then go to the next step.
5		No	Go to the next step.
6	INSPECT PURGE CONTROL SYSTEM OPERATION • Perform the "Purge Control System Operation Inspection". (See Purge Control System Inspection.) • Does purge control system operate properly?	Yes	Go to the next step.
6		No	Repair or replace malfunctioning part according to the inspection results. Then go to Step 11.
7	VERIFY CURRENT INPUT SIGNAL STATUS OF VSS • Connect the WDS or equivalent to the DLC-2. • Start the engine. • Access the VSS PID. • Inspect the VSS PID. (See PCM INSPECTION.) • Is the PID normal?	Yes	Go to the next step.
7		No	Inspect the malfunctioning part according to the inspection results. Then go to Step 11.
8	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 Step 11. (See ENGINE COOLANT TEMPERATURE (ECT) SENSOR REMOVAL/INSTALLATION.)
8		No	Go to the next step.
9	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 the Step 11. (See ECCENTRIC SHAFT POSITION SENSOR REMOVAL/INSTALLATION.)
9		No	Go to the next step.
10	IDENTIFY IF MALFUNCTION CAUSE IS CATALYTIC CONVERTER OR PCM • Make sure to reconnect all disconnected connectors. • Clear DTC from the PCM memory using the WDS or equivalent. • Perform the DRIVE MODE 1 and 3. (See OBD DRIVE MODE.) • Is the PENDING CODE P0420 present?	Yes	Replace the catalytic converter, then go to the next step.
10		No	Go to Step 12.
11	VERIFY TROUBLESHOOTING OF DTC P0420 COMPLETED • Make sure to reconnect all disconnected connectors. • Clear the DTC from the PCM memory using the WDS or equivalent. • Perform the DRIVE MODE 1 and 3. (See OBD 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.