Monitor Description
After engine is warmed up, the ECM performs air fuel ratio feedback control to regulate the air fuel ratio at stoichiometric ratio. In addition, this vehicle performs Active Air Fuel Ratio (A/F) Control for approximately 10 seconds after preconditions are met in order to measure the A/F sensor response rate. During active air fuel ratio control, the ECM forcibly increases and decreases the injection volume a certain amount based on learned stoichiometric air fuel ratio during usual air fuel feedback control, and measures the A/F sensor response rate. The ECM receives a signal from the A/F sensor while performing active A/F control and uses it to calculate the A/F sensor response rate deterioration level.
If the test value for A/F sensor response rate deterioration level is less than the threshold, ECM interprets this as a malfunction, and sets the DTC.