P0131

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) supplies a voltage of about 450 mV between the Heated Oxygen (HO2S) Sensor high and low signal circuits. The Oxygen (O2) sensor varies the voltage from approximately 1,000 mV when the exhaust is rich, through approximately 10 mV when the exhaust is lean.

The PCM monitors and stores the (HO2S) voltage information. The PCM evaluates the HO2S voltage samples in order to determine the amount of time the HO2S voltage was out of range. The PCM compares the stored HO2S voltage samples taken within each sample, period and determines if majority of the samples are out of the operating range.

The PCM monitors the HO2S voltage for being fixed below a predetermined voltage. If the PCM detects the voltage is below a predetermined voltage, a DTC sets.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0200, P0300 P0410, P0440, P0442, P0446, P0452, P0453, P1258, P1415, P1416, or P1441 are not set.
^ The ignition 1 signal is between 9-18 volts.
^ The loop status is Closed.
^ The secondary Air Injection (AIR) and the catalyst diagnostics are not active.
^ The Throttle Position (TP) is between 3-70 percent.
^ The Fuel Trim Learn is enabled.
^ The air fuel ratio is between 14.5-14.7 percent.
^ The fuel tank level remaining is more than 10 percent.

CONDITIONS FOR SETTING THE DTC
^ The HO2S signal voltage remains below 200 mV.
^ The conditions exist for 31 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.
^ Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS

IMPORTANT:
^ Before you service the PCM, remove any debris from the PCM connector surfaces. Inspect the PCM connector gaskets when you diagnose or replace the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent contaminant intrusion into the PCM.
^ For any test that requires probing the PCM or component harness connectors, use the J 35616-A connector test adapter kit. Using this kit prevents any damage to the harness connector terminals. Refer to Using Connector Test Adapters in Diagrams.

The PCM sets this DTC when the vehicle runs out of fuel. Inspect for the following conditions:
^ The Heated Oxygen Sensor (HO2S) wires-The sensor pigtail may be in contact with the exhaust manifold or the exhaust system.
^ The oxygen supply-An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provide the supply of oxygen. Inspect the HO2S wires and connections for breaks or for contamination. Refer to Heated Oxygen Sensor (HO2S) Wiring Repairs in Diagrams.
^ An intermittent ground-Inspect for an intermittent ground in the signal wire between the connector and the sensor.
^ Lean injectors-Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2, or refer to Fuel Injector Balance Test with Special Tool. Component Tests and General Diagnostics Component Tests and General Diagnostics
^ Fuel contamination-Water near the in-tank fuel pump inlet can be delivered to the injectors. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool). The water causes a lean exhaust and can set a DTC. Component Tests and General Diagnostics Component Tests and General Diagnostics
^ The fuel pressure-If the fuel pressure is too low, the system will be lean. Refer to Fuel System Diagnosis. Component Tests and General Diagnostics
^ Exhaust leaks-An exhaust leak near the HO2S can cause a lean condition. Refer to Exhaust Leakage in Exhaust System. Testing and Inspection
^ Vacuum or crankcase leaks can cause a lean condition.

If the above components are OK, the HO2S may be at fault.

For an intermittent condition, refer to Symptoms - Computers and Control Systems. Symptom Related Diagnostic Procedures

TEST DESCRIPTION

Steps 1-5:

Steps 6-13:

The numbers below refer to the step numbers on the diagnostic table.
2. If the HO2S voltage is fixed well below 200 mV, this indicates a short to battery ground or to chassis ground. If the voltage is fixed near or above 200 mV, this indicates a short to a PCM ground.

The engine must be at the normal operating temperature before performing this test.

3. Using the Freeze Frame/Failure Records data may help to locate an intermittent condition. If you cannot duplicate the DTC, the information in the Freeze Frame/Failure Records can help to determine how many miles have occurred since the DTC set. The Fail Counter and the Pass Counter can also help to determine the number of ignition cycles in which the diagnostic reported a pass and/or a fail. In order to isolate when the DTC failed, operate the vehicle within the same Freeze Frame conditions that the PCM recorded. These conditions include the RPM, the vehicle load, the vehicle speed, and the temperature.
4. A disconnected sensor should indicate a bias voltage. If the voltage is low, inspect the signal circuit for a short to ground.
5. Disconnecting the PCM allows using a DMM in order to test the circuit continuity. This procedure helps to locate an open or shorted circuit.