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 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 PCM commands the heater ON or OFF to maintain a specific HO2S operating temperature range. The PCM determines the temperature by measuring the current flow through the heater. When the heater is in the ON state, the PCM will pulse the heater OFF for a duration of 50 ms per second. When the heater is in the OFF state, the PCM will pulse the heater ON for a duration of 50 ms once per second. If the PCM detects that the HO2S 2 heater low control circuit current level is not within the calibrated range, DTC P0054 will set for bank 1 sensor 2.

The HO2S 2 has the following circuits:

• The HO2S 2 high signal circuit
• The HO2S 2 low reference circuit
• The HO2S 2 ignition 1 voltage circuit
• The HO2S 2 heater low control circuit