P0131

Diagnostic Chart:

Wiring Diagram:

Circuit Description

The Powertrain Control Module (PCM) supplies a voltage of about 0.45 volt between terminals C2-22 and C2-21 (if measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volt). The Oxygen Sensor (O2S 1) varies the voltage within a range of about 1 volt if the exhaust is rich, down through about 0.10 volt if the exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is below 315°C (600°F). An open sensor circuit or cold sensor causes Open Loop operation.

If the oxygen sensor pigtail wiring, connector or terminal are damaged, the entire oxygen sensor assembly must be replaced. DO NOT attempt to repair the wiring, connector or terminals. In order for the sensor to function properly, it must have a clean air reference provided to it. This clean air reference is obtained by way of the oxygen sensor wire(s). Any attempt to repair the wires, connectors or terminals could result in the obstruction of the air reference and degrade oxygen sensor performance.

Conditions for Setting the DTC

^ DTCs P0106, P0107, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0301, P0302, P0303, P0304, P0404, P0405, P0506, P0507, P1404, P1441 not set.

^ Engine run time is greater than 25 seconds.

^ Engine Coolant Temperature (ECT) is greater than 70°C (158°F).

^ Air/fuel ratio is between 14.5:1 and 14.7:1.

^ Engine is operating in Closed Loop.

^ Throttle Position (TP) angle is between 5% and 50%.

Or

^ Engine has met the above conditions for 20 seconds.

^ O2S 1 voltage is less than 43 mV for 125 seconds.

Action Taken When the DTC Sets

^ The Malfunction Indicator Lamp (MIL) will illuminate.

^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.

^ A history DTC is stored.

^ Coolant fan turns ON.

^ Vehicle will operate in Open Loop.

Conditions for Clearing the MIL/DTC

^ The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.

^ A history DTC will clear after 40 consecutive warm up cycles without a fault.

^ DTC(s) can be cleared by using the scan tool.

Diagnostic Aids

^ Fuel pressure - System will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving the vehicle at various road speeds and/or loads to confirm. Refer to Fuel System Diagnosis. System Diagnosis - Fuel System

^ MAP sensor - An output that causes the PCM to sense a lower than normal manifold pressure (high vacuum) can cause the system to go lean. Disconnecting the MAP sensor will allow the PCM to substitute a fixed (default) value for the MAP sensor. If the lean condition is gone when the sensor is disconnected, substitute a known good sensor and recheck. Refer to MAP Sensor Output Check. MAP Sensor Output Diagnosis

^ Fuel contamination - Water, in even small amounts, near the in-tank fuel pump inlet, can be delivered to the injector. The water causes a lean exhaust and can set DTC P0131.

^ Sensor harness - The O2S 1 sensor pigtail may be mis-positioned and contacting the exhaust manifold.

^ Engine misfire - A misfiring cylinder will result in unburned oxygen in the exhaust, which could cause DTC P0131. Refer to DTC P0300 P0300 Engine Misfire Detected and/or Symptoms. Testing and Inspection

^ Cracked Oxygen sensor (O2S 1) - A cracked O2S 1 or poor ground at the sensor could cause a DTC P0131. Refer to Symptoms. Testing and Inspection

^ Plugged fuel filter - A plugged fuel filter can cause a lean condition and cause a DTC P0131 to set.

^ Plugged Oxygen Sensor (O2S 1) - A plugged reference port on the Oxygen Sensor (O2S 1) will indicate a lower then normal voltage output from the O2S 1.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored in the scan tool for later reference.

2. This step determines if DTC P0131 is the result of a hard failure or an intermittent condition. It may be necessary to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction detected by the PCM.

4. This step simulates a DTC P0134. If the PCM senses the change, the PCM and wiring are OK.

6. The replacement PCM must be programmed and the crankshaft position system variation procedure must be preformed. Refer to the latest Tech line procedure for PCM reprogramming and also refer to Powertrain Control Module for the Crankshaft Position System Variation Procedure.

8. If no malfunctions have been found at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.