Air Fuel Ratio Sensor Control

ECM monitors the function of A/F sensor and the performance of catalyst.

ECM controls the A/F sensor according to the following sensors.

• A/F sensor (Oxygen level in the upstream of the catalyst)
• Heated oxygen sensor (Oxygen level in the downstream of the catalyst)

ECM determines the mean value of air-fuel ratio corrections according to a signal from the heated oxygen sensor and compares the determined value with the ECM-stored theoretical air-fuel ratio for optimal exhaust gas. If the multiple measurements deviate from the theoretical air-fuel ratio, a correction value for air-fuel mixture ratio control is determined. With the use of the correction value (the value of a new A/F sensor: approximately 0), the deterioration in A/F sensor can be corrected within a specified limit. Correction values are influenced by the characteristics map and the fuel injection time controlled by ECM.

Possible malfunctions occurring during the generation of air-fuel mixture are as follows.

• Air suction in the exhaust system due to leakage from the upstream of the heated oxygen sensor.
• Fuel injector wear or carbon accumulation
• Malfunction in A/F sensor/heated oxygen sensor
• Engine-related wear (e.g. worn-out valve)

If a correction value is outside the specified limit or an A/F sensor/heated oxygen sensor signal is inappropriate, ECM transmits a malfunction indicator lamp (MIL) signal to the combination meter via CAN communication.