Circuit Description

WARNING: This page is about a different car, the 2004 Buick Regal. 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 powertrain control module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once the sensor reaches operating temperature. A high HO2S voltage output indicates a rich fuel mixture. A 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 provide an accurate voltage signal. The PCM monitors the HO2S activity to make sure enough lean-to-rich and rich-to-lean switches occur. This diagnostic runs once per trip. If the PCM detects that the HO2S 1 voltage did not switch enough times during a calibrated time period, DTC P1133 will set.

Each HO2S 1 has the following circuits:

An HO2S 1 high signal circuit
An HO2S 1 low signal circuit
An HO2S 1 heater ignition voltage circuit
An HO2S 1 heater low control circuit
An HO2S low reference circuit