P0131
Schematic:
CIRCUIT DESCRIPTION
The PCM supplies a bias voltage of about 450mV between the HO2S signal and low circuits. When measured with a 10 megohm digital voltmeter, this may display as low as 350 mV. The oxygen sensor varies the voltage within a range of about 1000 mV when the exhaust is rich, down through about 100 mV when exhaust is lean. The PCM constantly monitors the HO2S signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing injector pulse width as necessary. If the HO2S 1 voltage remains excessively low for an extended period of time, DTC P0131 will be set.
CONDITIONS FOR RUNNING THE DTC
^ None of the following active DTCs are present:
- Throttle Position (TP) sensor
- Evaporative Emissions (EVAP) system
- Misfire
- Intake Air Temperature (IAT) sensor
- Manifold Absolute Pressure (MAP) sensor
- Fuel trim
- Fuel injector circuit
- EGR pintle position
- Engine Coolant Temperature (ECT) sensor
- Crankshaft Position (CKP) sensor
- Mass Air Flow (MAF) sensor
^ The system voltage is more than 9 volts.
^ The closed loop commanded air/fuel ratio is between 14.5:1 and 14.8:1.
^ The throttle angle is between 3 percent and 40 percent.
CONDITIONS FOR SETTING THE DTC
^ The HO2S 1 signal voltage remains less than 175 mV during normal closed loop operation, or
^ the HO2S 1 signal voltage remains less than 600 mV during power enrichment mode fuel control operation.
^ Either condition is present for up to 60 seconds.
ACTION TAKEN WHEN THE DTC SETS
^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.
^ If the misfire is determined to be catalyst damaging, the PCM will flash the MIL.
CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.
^ The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using a scan tool.
DIAGNOSTIC AIDS
Check for the following conditions:
^ The heated oxygen sensor pigtail may be routed incorrectly and contacting the exhaust system.
^ Any faulty PCM to engine block grounds, refer to Ground Distribution Schematics.
^ The fuel system will go lean if the fuel pressure is too low. The PCM can compensate for some decrease. However, if the fuel pressure is too low, a DTC P0131 may be set. Refer to the appropriate procedure:
- Fuel System Pressure Test Fuel System Pressure Test
^ Correct fuel injector operation. Refer to Fuel Injector Coil Test - Engine Coolant Temperature (ECT) Between 10-35 Degrees C (50-95 Degrees F) or Fuel Injector Coil Test - Engine Coolant Temperature (ECT) Outside 10-35 Degrees C (50-95 Degrees F). Component Tests and General Diagnostics Component Tests and General Diagnostics
^ Check for the following vacuum conditions:
- Any disconnected or damaged vacuum hoses Refer to Emission Hose Routing Diagram.
- An incorrectly installed or malfunctioning crankcase ventilation valve, refer to the appropriate procedure:
^ Crankcase Ventilation System Inspection Positive Crankcase Ventilation
- Vacuum leaks at the throttle body, the EGR valve, and the intake manifold mounting surfaces
^ An exhaust leak may cause outside air to be pulled into the exhaust gas stream past the HO2S, causing the system to appear lean. Check for exhaust leaks that may cause a false lean condition to be indicated.
^ Check the throttle body inlet screen for damage or objects that may alter the airflow sample through the MAF sensor. If a problem is found, correct as necessary. Refer to Throttle Body Air Inlet Screen Replacement.
^ Disconnect the MAF sensor. If the lean condition is corrected with the MAF sensor disconnected, replace the MAF sensor. Refer to MAF Sensor Replacement.
^ Check for fuel contamination. Water, even in small amounts, can be delivered to the fuel injectors. The water can cause a lean exhaust to be indicated. Excessive alcohol in the fuel can also cause this condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis. Component Tests and General Diagnostics
^ If none of the above conditions are present, replace the affected HO2S. Refer to Heated Oxygen Sensor (HO2S) Replacement (Bank 1 Sensor 1) or Heated Oxygen Sensor (HO2S) Replacement (Bank 1 Sensor 2).
TEST DESCRIPTION
Diagnostic Chart:
The numbers below refer to step numbers on the diagnostic table.
3. This DTC failing during power enrichment operation (TP angle more than 60 percent) may indicate a condition described in Diagnostic Aids. If this DTC test passes while the Fail Records conditions are being duplicated, an intermittent condition is indicated. Review the Fail Records vehicle mileage since the diagnostic test last failed. This may help determine how often the condition that caused the DTC to be set occurs.
6. This vehicle is equipped with a PCM which utilizes an electrically Erasable Programmable Read-only Memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.