Monitor Description

The ECM uses the heated oxygen sensor to optimize the air/fuel mixture in 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 conditions for closed-loop fuel control are met and after a specified time-period, the sensor's output signal never indicates RICH, the ECM will conclude that closed loop fuel control is malfunctioning. The ECM will illuminate the MIL and a DTC is set.