Circuit Description

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 in Closed Loop. 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 calculates a transition time ratio for rich-to-lean and lean-to-rich HO2S voltage switches. If the PCM detects that the calculated transition time ratio is incorrect, DTC P1134 will set.

The HO2S 1 has the following circuits:

• HO2S 1 high signal
• HO2S 1 low reference
• HO2S 1 heater ignition voltage
• HO2S 1 heater low control
• Low reference loop