P0131

Diagnostic Chart:

Wiring Diagram:

The oxygen sensor (02S) 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 oxygen sensor signal and adjusts the fuel mixture accordingly.

DTC PARAMETERS

DTC P0131 will set if the 025 voltage is less than 87mV for 90 seconds.

OR

02S voltage is less than 300 mV in Power Enrichment (PE) mode for 30 seconds when:

^ The system is in closed loop mode.
^ No other engine sensor or misfire DTCs have been set.
^ Commanded A/F ratio is approximately 14.7 to 1.

NOTE: The 02S signal is continuously checked once the above conditions are met.

DIAGNOSTIC AIDS

When attempting to diagnose an intermittent problem use the Scan tool to review malfunction history information. The supplemental data can be used to duplicate a problem.

Intermittents or opens suspected to be at the connector can be detected by using diagnostic service probe Voltage can be read on wires without disconnecting any connectors.

Check the tightness of the female terminal grip with a spare male terminal.

POSSIBLE CAUSES:

If the system is commanding rich (engine running lean), the oxygen sensor signal is around 100 mv and short term fuel trim (integrator) is in the 160s, the system is nearing or at maximum correction.

Review Scan tool malfunction history WOT lean fault. A total of 30 seconds under power enrichment mode (PE) per ignition cycle will set a WOT lean fault to Yes if a lean condition occurs. Check the following for possible low 02S voltage:

^ Low fuel pressure.
^ Malfunctioning sensor.
^ External water on sensor.
^ Sensor wire shorted to ground.