Code 44, Oxygen (O2) Sensor Circuit (Lean Exhaust Indication): Notes

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

The oxygen sensor varies voltage within range of approximately .1 volt (lean exhaust) to 1 volt (rich exhaust). The sensor is like an open circuit and produces no voltage when sensor temperature is less than 600°F (316°C). An open sensor circuit or cold sensor causes open loop operation.

Code 44 is set when oxygen (O2) sensor voltage on circuit No. 412 remains less than .3 volt for about one minute, and the system is operating in closed loop.