Circuit Description

The Engine Control Module (ECM) supplies a voltage of about 0.45 V between the ECM terminals A8 and A12. The Oxygen (O2) sensor varies the voltage within a range of about 1 V if the exhaust is rich, down to about 0.1 V if the exhaust is lean. The O2 sensor is like an open circuit and produces no voltage when it is below 360 °C (680 °F). An open O2 sensor circuit or a cold O2 sensor causes "Open Loop" operation.