Theory Of Operation

The Oxygen sensors (O2 sensor) are used for fuel control and catalyst monitoring. Each O2 sensor compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the O2 sensor signal voltage while calculating the air-to-fuel ratio. The heating elements inside each O2 sensor heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the PCM to calculate the air-to-fuel ratio sooner. While the engine runs, the O2 sensor heats up and begins to generate a voltage within a range of 0-1, 275 mV. Once sufficient O2 sensor voltage fluctuation is observed by the PCM, Closed Loop is entered. The PCM uses the O2 sensor voltage to determine the air-to-fuel ratio. An O2 sensor voltage that increases toward 1, 000 mV indicates a rich fuel mixture. An O2 sensor voltage that decreases toward 0 mV indicates a lean fuel mixture.