Theory Of Operation

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This vehicle is equipped with a 5-wire wide-band O2 Sensor. This sensor operates differently from traditional O2 Sensors. The wide-band O2 Sensor tip consists of two cells that provide different functions, a measurement chamber and a detection chamber with pumping capabilities. The oxygen pumping function is the ability to pump oxygen into or out of the measurement chamber depending on the level of oxygen in the measurement chamber. This function provides the wide-band sensing capabilities and is critical for proper oxygen measurement.

The Oxygen (O2) Sensor is used for fuel control and catalyst monitoring. The O2 Sensor measures 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 the O2 Sensor heats the sensor to bring it 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 specified range. 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. The PCM makes short-term and long-term corrections to maintain stoichiometric air/fuel ratio for best catalytic converter efficiency. Short-term fuel correction is based directly on the O2 Sensor feedback and is designed for quick engine response. The long-term fuel correction compensates for variations in the engine specifications, sensor tolerances, and component aging. The PCM calculations of this feedback are designed to correct rich and lean conditions over a longer period of time. For an aged O2 Sensor, the response rate to air/fuel changes is slower than when it was new. The O2 Sensor tends to move less with the same air/fuel changes in a given time frame. Therefore, by observing the activity of voltage readings (from the O2 Sensor), the quality of the sensor can be detected.