Code 45, Oxygen (O2) Sensor Circuit (Rich Exhaust Indication)

The ECM supplies a voltage of about .45 volt between terminals D7 and D6. If measured with 10-megohm digital voltmeter, this may read as low as .32 volt.

The oxygen sensor varies the voltage within a range of about one volt, if the exhaust is rich, down to about .10 volt if the exhaust is lean. The sensor is like an open circuit and produces no voltage when sensor temperature is less than below 600°F (316°C). An open sensor circuit or cold sensor causes "open loop" operation.

Code 45 is set when O2 sensor voltage on circuit No. 412 remains greater than .8 volt for one minute and system is in "closed loop".