Monitor Description
The ECM uses sensors mounted in front of and behind the front catalyst to monitor its efficiency.
The first sensor, the air fuel ratio sensor, sends pre-catalyst information to the ECM. The second sensor, the heated oxygen sensor, sends post-catalyst information to the ECM.
In order to detect any deterioration in the three-way catalytic converter, the ECM calculates the Oxygen Storage Capacity (OSC) of the three-way catalytic converter. This calculation is based on the voltage output of the heated oxygen sensor while performing active air-fuel ratio control.
The OSC value is an indication of the oxygen storage capacity of the three-way catalytic converter. 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 the rich-lean cycle of the heated oxygen sensor is long, the OSC becomes greater. There is a direct correlation between the OSCs of the heated oxygen sensor and three-way catalytic converter.
The ECM uses the OSC value to determine the state of the three-way catalytic converter. If any deterioration has occurred, it illuminates the MIL and stores the DTC.
| DTC No. | DTC Detection Condition | Trouble Area |
|---|---|---|
| P0420 | OSC value is less than the standard value under active air-fuel ratio control (2 trip detection logic). |
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| P0430 | OSC value is less than the standard value under active air-fuel ratio control (2 trip detection logic). |
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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.