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 Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Engine Control Module (ECM) operates in an open loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The ECM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates greater than and less than bias voltage. High HO2S voltage output indicates a rich fuel mixture. Low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The ECM monitors the rich-to-lean and lean-to-rich transition time. If the ECM detects an HO2S 1 voltage signal that remains at or near the bias voltage, DTC P0134 will set for HO2S Bank 1; Sensor 1 or DTC P0154 will set for HO2S Bank 2; Sensor 1.