P0131

CIRCUIT DESCRIPTION
The powertrain control module (PCM) supplies a voltage of about 450 mV between the heated oxygen sensor (HO2S) high and low signal circuits. The oxygen sensor (O2) 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 the 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, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, 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 fuel tank level remaining is more than 10 percent.
^ The loop status is closed.
^ Intrusive tests are not in progress.
^ Scan tool output controls are not active.

Lean Test Enable
^ The air fuel ratio is between 14.5:1 and 14.7:1.
^ The throttle position (TP) is between 3-70 percent.

Power Enrichment Test Enable
^ Power enrichment is active.
^ The above condition is met for 1 second.

CONDITIONS FOR SETTING THE DTC

Lean Test
The HO2S voltage is less than 200 mV for 165 seconds.

Power Enrichment Test
The HO2S voltage is less than 360 mV for 10 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.
^ The control module commands Open Loop.

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

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 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. Exhaust Leakage
^ 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 Controls Systems. Symptom Related Diagnostic Procedures

TEST DESCRIPTION

Steps 1-4:

Steps 5-13:

The numbers below refer to the step numbers on the diagnostic table.
2. If the voltage is below the specified value, the condition is present.
4. A disconnected sensor should indicate a bias voltage. If the voltage is low, inspect the signal circuit for a short to ground.