Circuit Description

The engine control module (ECM) supplies a voltage of about 0.45 V between the ECM terminals 27 and 67. The oxygen (02) 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 02 sensor is like an open circuit and produces no voltage when it is below 360 °C (600 °F). An open 02 sensor circuit or a cold 02 sensor causes "open loop" operation.