Circuit Description

WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

Heated Oxygen Sensor (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The Engine Control Module (ECM) supplies the HO2S with a reference or bias voltage of about 450 mV. When the engine is first started the ECM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.

This diagnostic will only run once per ignition cycle. The ECM monitors the rich-to-lean and lean-to-rich transitions. A transition is defined as the HO2S voltage changes from greater than 600 mV to less than 300 mV or from less than 300 mV to greater than 600 mV. If ECM detects that the transition time ratio is not within a specified range, DTC P1134 will set.