Monitor Description

The ECM uses the heated oxygen sensor to optimize the air-fuel mixture in the closed-loop fuel control. This control helps decrease exhaust emissions by providing the catalyst with a nearly stoichiometric mixture.

The sensor detects the oxygen level in the exhaust gas and the ECM uses this data to control the air-fuel ratio. The sensor output voltage ranges from 0 V to 1 V. If the signal voltage is less than 0.4 V, the air-fuel ratio is LEAN. If the signal voltage is more than 0.5 V, the air-fuel ratio is RICH. If the sensor does not indicate RICH even once despite the conditions for the closed-loop fuel control being met and a specified time period has passed, the ECM will conclude that the closed-loop fuel control is malfunctioning. The ECM will illuminate the MIL and a DTC is set.