Oxygen Sensor: Description and Operation

Oxygen Sensor (Typical):

PCM Wiring:

The ECM/PCM provides a 0.45 volt reference signal to the oxygen sensor. When the oxygen sensor is cold (below 200°C), the oxygen sensor signal voltage will be around 0.45 volts and the ECM/PCM will keep the system in open loop operation. When the oxygen sesor is warm (above 200°C), the oxygen sensor will swing from rich to lean (above and below 0.45 volts) rapidly, at least one swing every two seconds, if the PCM is in good control of the air fuel mixture.

The oxygen sensor is mounted in the exhaust system where it can monitor the oxygen content of the exhaust gas stream. The oxygen sensor acts as an electro-chemical cell or battery. A voltage is produced in response to the amount of oxygen in the exhaust stream, compared to the oxygen content in the atmosphere. A lean mixture, high O2 content in the exhaust, will produce a low voltage. A rich mixture, low O2 content in the exhaust, will produce a high voltage. Oxygen sensor voltages range from approximately 100 millivolts to 900 millivolts. By monitoring the voltage output of the 02 sensor, the PCM/ECM will determine what fuel mixture command to send to the injectors. All models have two oxygen sensors (right and left).

The oxygen sensor, if open, should set a code E013 or E017. A shorted sensor circuit to ground should set a code E042 or code E044. A sensor circuit shorted to voltage should set a code E043 or code E045. When any of these codes are set, the car will run in open loop.

A code E042, E043, E044 or E045 usually indicates rich or lean engine operation, rather than a defective oxygen sensor or circuit.