P0131

DTC P0131 Oxygen Sensor 1 (O2S1) Low Voltage

Circuit Diagram:

Circuit Description
The Engine Control Module (ECM) supplies a voltage of about 0.45 volts between terminals M12 and M29 (if measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volts). The Oxygen sensor 1 (O2S1) varies the voltage within a range of about 1 volt if the exhaust is rich, down through about 0.10 volts 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 O2S1 pigtail wiring, connector, or terminal is damaged, the entire O2S1 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 O2S1 wire(s). Any attempt to repair the wires, connector or terminals could result in the obstruction of the air reference and degrade the O2S1 performance. Refer to "Oxygen sensor 1".

Conditions for Setting the DTC
- O2S1 voltage is less than 0.05 volts.
- Closed loop stoichiometry.
- Engine Coolant Temperature (ECT) is greater than 60 °C (140 °F).
- System voltage is greater than 10 volts.
- DTCs P0106, P0107, P0108, P0117, P0118, P0122, P0123, P0171, P0172, P0201, P0202, P0203, P0204, P0300, P0336, P0337, P0351, P0352, P0401, P0402, P0404, P0405, P0406, P0502, P0506, P0507, P1404, P1441, and P0443 are not set.
- 3 second delay after conditions are met.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The ECM 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.
- The vehicle will operate in Open Loop.

Conditions for Clearing the MIL/DTC
- The MIL will turn off after four 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.
- The DTC(s) can be cleared by using the scan tool.
- Disconnecting the ECM battery feed for more than 10 seconds.

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

Manifold Absolute Pressure (MAP) sensor - An output that causes the ECM to sense a lower than normal manifold pressure (high vacuum) can cause the system to go lean. Disconnecting the MAP sensor will allow the ECM 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. 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 O2S1 sensor pigtail may be out of position and contacting the exhaust manifold. Engine misfire - A misfiring cylinder will result in unburned oxygen in the exhaust, which could cause DTC P0131 to set. Refer to DTC P0300 Engine Misfire.

Cracked Oxygen sensor 1 - A cracked O2S1 or poor ground at the sensor could cause DTC P0131. Refer to Symptom Diagnostic Table. Important Preliminary Checks
Plugged Oxygen sensor 1 - A plugged reference port on the O2S1 will indicate a lower-than-normal voltage output from the O2S1.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
1. The On-Board Diagnostic (OBD II) 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 on 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 ECM.
4. This step simulates DTC P0134. If the ECM senses the change, the ECM and the wiring are OK.
6. The replacement ECM must be reprogrammed. Refer to the latest Techline procedure for ECM reprogramming.
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.

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