Circuit Description

The engine control module (ECM) supplies a voltage of about 0.45V between the ECM terminals 27 and 67. The oxygen (O2) sensor varies the voltage within a range of about 1V if the exhaust is rich, down to about 0.1V if the exhaust is lean. The O2 sensor is like an open circuit and produces no voltage when it is below 360°C (600°F). An open O2 sensor circuit or a cold O2 sensor causes "open loop" operation.