Monitor Description

The ECM uses sensors mounted in front of and behind the Three-Way Catalytic Converter (TWC) to monitor its efficiency.

The first sensor, the Air-Fuel Ratio (A/F) sensor, sends pre-catalyst information to the ECM. The second sensor, the Heated Oxygen (HO2) sensor, sends post-catalyst information to the ECM. In order to detect any deterioration in the TWC, the ECM calculates the Oxygen Storage Capacity (OSC) of the TWC. This calculation is based on the voltage output of the HO2 sensor while performing active air-fuel ratio control, rather than the conventional detecting method, which uses the locus ratio. The OSC value is an indication of the oxygen storage capacity of the TWC. When the vehicle is being driven with a warm engine, active air-fuel ratio control is performed for approximately 15 to 20 seconds. When it is performed, the ECM deliberately sets the air-fuel ratio to lean or rich levels. If a rich-lean cycle of the HO2 sensor is long, the OSC becomes greater. There is a direct correlation between the OSCs of the HO2 sensor and the TWC.

The ECM uses the OSC value to determine the state of the TWC. If any deterioration has occurred, it illuminates the MIL and sets a DTC.

DTC No.

DTC Detection Conditions

Trouble Areas

P0420

OSC value smaller than standard value under active air-fuel ratio control (2 trip detection logic)

• Gas leakage from exhaust system

• Exhaust manifold (TWC)

P0430

OSC value smaller than standard value under active air-fuel ratio control (2 trip detection logic)

• Gas leakage from exhaust system

• Exhaust manifold (TWC)

HINT:

• Bank 1 refers to the bank that includes cylinder No. 1.

• Bank 2 refers to the bank that does not include cylinder No. 1.

• Sensor 1 refers to the sensor closest to the engine assembly.

• Sensor 2 refers to the sensor farthest away from the engine assembly.

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