P0420

Wiring Diagram:

CIRCUIT DESCRIPTION

The system uses a three-way catalytic converter in order to control the emissions of Hydrocarbons (HC), Carbon Monoxide (CO) and Oxides of Nitrogen (NOx). The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The Vehicle Control Module (VCM) has the capability to monitor this process using the HO2S (Bank 1, Sensor 1). The HO2S (Bank 1, Sensor 3), located in the exhaust downstream of the three-way catalytic converter, produces an output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalysts ability to convert exhaust emissions effectively. If the catalyst is functioning correctly, the HO2S (Bank 1, Sensor 3) signal will be far less active than that produced by the HO2S (Bank 1, Sensor 1). If a problem exists which causes the VCM to detect an excessive HO2S (Bank 1, Sensor 3) activity outside of an acceptable range for an extended period of time, the VCM sets the DTC P0420. This DTC indicates that the three-way catalytic converters oxygen storage capacity is below a threshold considered acceptable.


CONDITIONS FOR SETTING THE DTC Converter Warm Up Test Enable

^ Engine in closed loop.

^ Commanded air fuel ratio equals 14.7.

^ The engine run time equals 346 seconds.

^ The Intake Air Temperature (IAT) is between -6.75-75°C (20-167°F).

^ The Engine Coolant Temperature (ECT) is between 75-117°C (167-243°F).

^ BARO equals 73 kPa.

^ The Predicted Catalyst Temperature is greater than or equal to 475°C (809°F).

^ The Throttle Position (TP) sensor is no more than 1.7%.

^ Engine idling at or near the recommended speed.

^ The Vehicle Speed Sensor (VSS) is no more than 1 mph.

^ No VSS DTCs.

^ No transmission DTCs.

^ No TP DTCs.

^ No purge DTCs.

^ No Idle Air Control (IAC) DTCs.

^ No HO2S DTCs.

^ No EVAP DTCs.

^ No misfire DTCs.

^ No EGR DTCs.

^ No ECT DTCs.

^ No Camshaft Position (CMP) DTCs.

^ No MAP DTCs.

^ No fuel trim DTCs.

^ No Ignition Control (IC) DTCs.

^ No IAT sensor DTCs.

^ No Mass Air Flow (MAF) sensor DTCs.


ACTION TAKEN WHEN THE DTC SETS

The VCM will turn ON the Malfunction Indicator Lamp (MIL).

CONDITIONS FOR CLEARING THE MIL/DTC

^ The VCM turns the MIL OFF after 3 consecutive drive trips when the test has Run and Passed and not Failed.

^ A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle).

^ Use the scan tool Clear Information function.

^ Disconnect the VCM battery feed for 30 seconds.


DIAGNOSTIC AIDS

Difficulty running the OBD II status DTC P0420 test may be encountered in areas where the test conditions cannot be maintained easily, especially in urban areas.


TEST DESCRIPTION

The numbers below refer to the step numbers on the diagnostic table.

2. Ensures that the fault is present.

6. Ensures that the knock sensor is capable of detecting detonation.