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 to provide an accurate voltage signal. The PCM controls the HO2S 2 heater low control circuit with a low side driver. The HO2S 2 heater diagnostic monitors the amount of time it takes for the HO2S 2 to generate a voltage that is higher or lower than bias voltage by a calibrated amount. If the PCM detects that the HO2S 2 voltage has not changed more than 74 mV from bias voltage within a calibrated amount of time, DTC P0141 will set.

Each HO2S 2 has the following circuits:

An HO2S 2 high signal circuit
An HO2S 2 low reference circuit
An HO2S 2 heater ignition voltage circuit
An HO2S 2 heater low control circuit
An HO2S low reference circuit