Heated Oxygen Sensors (Pre-Catalyst)

The main function of the Pre-Catalyst Heated Oxygen Sensor (HO2S) is to provide the PCM with exhaust stream information in order to maintain proper fueling to hold emissions within acceptable levels. These oxygen sensors are always located between the exhaust manifold and the catalytic converter. After the sensor reaches the operating temperature, the sensor generates a voltage inversely proportional to the amount of oxygen present in the exhaust gases.

The PCM uses the signal voltage from the fuel control heated oxygen sensors in a closed loop in order to adjust the fuel injector pulse width. While in a closed loop, the PCM can adjust fuel delivery in order to maintain an air to fuel ratio which allows the best combination of emission control and driveability.

If the oxygen sensor pigtail wiring, connector or terminal are damaged, replace the entire oxygen sensor assembly. Do not attempt to repair the wiring, connector, or terminals. In order for the sensor to function properly, the sensor must have a clean air reference provided to it. This clean air reference is obtained by way of the oxygen sensor wires. Any attempt to repair the wires, connectors or terminals could result in the obstruction of the air reference. Any attempt to repair the wires, connectors or terminals would degrade oxygen sensor performance.