Circuit Description

Oxygen Sensors (O2S) are used for fuel control and post catalyst monitoring. Each O2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The O2S must reach operating temperature to provide an accurate voltage signal. A heating element in O2S 2 minimizes the time required for the sensor to reach operating temperature. The PCM supplies the O2S with a reference or bias voltage of about 450 mV. When engine is first started, PCM operates in open loop, ignoring the O2S voltage signal. Once the O2S reaches operating temperature and Closed Loop is achieved, the O2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage. High O2S voltage indicates a rich exhaust stream. Low O2S voltage indicates a lean exhaust stream.

This diagnostic will only run once per ignition cycle. The PCM monitors the rich-to-lean and lean-to-rich transition time. A transition is defined as, the O2S voltage changes from greater than 600 mV to less than 300 mV or from less than 300 mV to greater than 600 mV. If PCM detects that the transition time is too long, DTC P0133 will set.