45 Rich Oxygen Sensor Signal

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The Oxygen (O2) 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 318°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 45 will set if:

  • The system is in closed loop mode.
  • TPS in a 2 to 20% range.
  • Oxygen sensor is greater than 750 mV for 30 seconds.
  • Codes 33 - 34 are 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.

Possible Causes

  • Fuel pressure high.
  • Leaking injector.
  • Canister purge.
  • Oxygen sensor contamination.
  • EGR valve.
  • Engine oil contamination.
  • Shorted injector.
  • Vacuum leak to map sensor.