Catalyst Efficiency Monitor Function
The catalyst efficiency monitor function is performed when the following conditions are satisfied.
- The three way catalyst temperature is in operating temperature range
- The air-fuel ratio correction control satisfies the operating conditions
The catalyst efficiency monitor function that the air-fuel ratio correction control satisfies the operating conditions monitors the degree of deterioration in catalyst and that of hydrocarbon conversion according to the oxygen adsorption rate of catalyst.
ECM monitors the catalyst efficiency according to the following sensors.
- Crankshaft position sensor (Engine speeds)
- Air-fuel ratio (A/F) sensor
- Heated oxygen sensor
Oxygen of the catalyst is stored when air-fuel mixture is lean and reduced when air-fuel mixture is rich.
Due to high oxygen adsorption amount of the three-way catalyst, exhaust emissions decrease, and accordingly, oxygen content in the downstream of catalyst becomes almost steady. Accordingly, the signal amplitude of the O2 sensor is reduced and almost steady.
When the three-way catalyst reaches the operating temperature and the air-fuel ratio correction starts, the signal amplitude of air-fuel ratio sensor upstream of the three-say catalyst is compared to that of the O2 sensor downstream of the three-way catalyst. When three-way catalyst does not function, the signal amplitude of air-fuel ratio sensor and O2 sensor becomes equal. Multiple measurements are performed in the low load area within the specified engine speeds. ECM compares the measurement results with the characteristics map. When a malfunction is detected in the catalyst based on the comparison, ECM requests the combination meter to turn ON the malfunction indicator lamp (MIL) and records the malfunction.