Oxygen Sensors

Heated Oxygen Sensors (HO2S) are used for fuel control (HO2S 1) and post catalyst monitoring (HO2S 2). 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 0-1000 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 provide an accurate voltage signal. If the PCM detects an active HO2S signal of a higher or lower than calibrated minimum amplitude, for a excessive amount of time, voltage average response time is too slow, remains below, at, or near the bias voltage amount, a DTC will set.

Each HO2S has the following circuits:

• HO2S high signal
• HO2S low signal
• HO2S heater ignition 1 voltage
• HO2S heater ground

Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. The HO2S heater performance diagnostic will only run from a cold start and only once per key cycle. This DTC will set if the HO2S 1 heater takes too long to heat based on the HO2S signal voltage input to the PCM. The HO2S heater circuit is energized anytime the ignition key is in the RUN position. If the PCM detects that the HO2S heater takes too long to heat, based on the HO2S signal voltage, a DTC will set.