P0131

CIRCUIT DESCRIPTION
The powertrain control module (PCM) supplies a voltage of approximately 0.45 volt between the heated oxygen sensor (HO2S) high signal and the low signal circuit. The HO2S 1 varies the voltage within a range of approximately 1 volt if the exhaust is rich, to approximately 0.10 volt if the exhaust is lean.

The sensor is like an open circuit and does not produce any voltage if the temperature is less than 315°C (600°F). An open sensor circuit or a cold sensor causes an Open Loop operation.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, P0172, P0201-P0204, P0300, P0301-P0304, P0335, P0440, P0442, P0446, P0506, P0507, P0601, P0602, or P1441 are not set.
^ The coolant temperature is greater than 70°C (158°F).
^ The battery voltage is greater than 10 volts.
^ The minimum fuel level is greater than 10 percent.
^ The engine run time is greater than 10 seconds.
^ The engine is operating in Closed Loop.
^ The throttle position (TP) angle is between 8-50 percent.
^ The manifold absolute pressure (MAP) is greater than 25 kPa.
^ The engine has been in the above conditions for 4 seconds.

CONDITIONS FOR SETTING THE DTC
HO2S 1 voltage is less than 52 mV for 125 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
^ Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS
^ The fuel pressure-The system will be lean if the fuel pressure is too low. You may need to monitor fuel pressure while driving the vehicle at various road speeds and/or loads in order to confirm this condition. Refer to the Fuel System Diagnosis. Component Tests and General Diagnostics
^ The manifold absolute pressure (MAP) sensor- An output that causes the PCM to sense a lower than normal manifold pressure, or a high vacuum, can cause the system to go lean. Disconnecting the MAP sensor will allow the PCM to substitute a fixed, or a default, value for the MAP sensor. If the lean condition is gone when the MAP sensor is disconnected, refer to DTC P0105 for further diagnosis. P0105
^ Fuel contamination-Even small amounts of water near the in-tank fuel pump inlet can be delivered to the injector. The water causes a lean exhaust and can set DTC P0131.
^ The sensor harness-The HO2S 1 sensor pigtail may be mis-positioned and contacting the exhaust manifold.
^ An engine misfire-A misfiring cylinder will result in unburned oxygen in the exhaust, which could cause DTC P0131. Refer to DTC P0300 or Symptoms - Computers and Control Systems. P0300 Symptom Related Diagnostic Procedures
^ A cracked HO2S 1-A cracked HO2S 1 or a faulty ground at the HO2S could cause DTC P0131. Refer to Symptoms - Computers and Control Systems. Symptom Related Diagnostic Procedures
^ A plugged fuel filter-A plugged fuel filter can cause a lean condition and cause DTC P0131 to set.
^ A plugged HO2S-A plugged reference port on the HO2S will indicate a lower than normal voltage output from the HO2S.

TEST DESCRIPTION

DTC P0131 - Steps 1-9:

DTC P0131 - Steps 10-11:

The number below refers to the step number on the diagnostic table.
2. This step determines if the DTC P0131 is the result of a hard malfunction or an intermittent condition. You may need to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction that was detected by the PCM.