44 Lean Oxygen Sensor Signal

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Description

The oxygen (02) sensor consists of a zirconia electrolyte between two platinum plates. When the sensor reaches approximately 318°C (600°F) it becomes an electrical source that responds to the oxygen content in the exhaust. The PCM produces a bias voltage of approximately 450 millivolts on the oxygen sensor circuit. When the sensor is cold its internal resistance is extremely high therefore the PCM recognizes the bias as an open circuit. As the sensor warms up, the internal resistance decreases. When the sensor reaches approximately 315°C (600°F), it starts producing a voltage based on the oxygen content in the exhaust stream. This voltage is used by the PCM to determine a rich or lean signal and adjust the fuel mixture accordingly.

Code Parameters

Code 44 will set if:

  • The system is in closed loop mode.
  • Oxygen sensor is less than 300 mV for more than 3 minutes.
  • Codes 33 - 34 not present.

Diagnostic Aids

  • When attempting to diagnose an intermittent problem use the Scan Tool to review supplemental diagnostic information. The supplemental data can be used to duplicate a problem. Select MALF History from Scan Tool EC menu.
  • Check the tightness of the female terminal grip with a spare male terminal.

Possible Causes

  • Misfiring cylinders (see Ignition System section).
  • Running out of fuel.
  • Low fuel system pressure.
  • Water on sensor.
  • Plugged injector.
  • Engine stalling while vehicle is moving.