Monitor Description
The ECM uses the two 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 (sensor 1), sends pre-catalyst information to the ECM.
The second sensor, the Heated Oxygen (HO2) sensor (sensor 2), sends post-catalyst information to the ECM. The ECM compares the information transmitted by these two sensors to determine the efficiency of the TWC performance and its ability to store oxygen.
When the TWC is functioning properly, the variation in the oxygen concentration in the exhaust gas, after it has passed through the TWC, is small. As a result, the voltage output of sensor 2 slowly alternates between the rich and lean signal voltages (shown in the illustration below). As the TWC performance efficiency deteriorates, its oxygen storage capacity decreases, and the variation in the oxygen concentration in the exhaust gas increases. As a result, the sensor voltage output fluctuates frequently. While the catalyst monitor is running, the ECM measures the signal length of both sensors 1 and 2, and calculates the ratio of the signal lengths to determine the extent of the TWC deterioration. If the deterioration level exceeds the preset threshold, the ECM interprets this as the TWC malfunction. The ECM then illuminates the MIL and sets the DTC.
| DTC No. | DTC Detection Condition | Trouble Area |
|---|---|---|
| P0420 | After engine and TWC warmed up, and while vehicle driven within set vehicle and engine speeds, waveform of Heated Oxygen (HO2) sensor (bank 1 sensor 2) alternates frequently between rich and lean (2 trip detection logic) |
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| P0430 | After engine and catalyst are warmed up, and while vehicle is driven within set vehicle and engine speed ranges: Waveform of heated oxygen sensor (bank 2 sensor 2) alternates frequently between rich and lean (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.