P0131
CIRCUIT DESCRIPTIONThe Heated Oxygen Sensor (HO2S) is a sensor used to detect the oxygen content in the exhaust. The Powertrain Control Module (PCM) supplies the sensor with a signal circuit and a ground circuit. The PCM supplies a bias voltage between the circuits. The sensor varies the voltage based on the oxygen content in the exhaust. When the exhaust stream is lean, indicating more oxygen, the sensor produces a low voltage signal. When the exhaust stream is rich, indicating less oxygen, the sensor produces a high voltage signal. The PCM monitors the HO2S signal during Closed Loop. In order to correct for rich or lean conditions, the PCM adjusts the injector pulse width. This Diagnostic Trouble Code (DTC) indicates that the HO2S voltage remained too low for a calibrated period of time.
CONDITIONS FOR RUNNING THE DTC
^ DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0201-P0208, P0410, P0412, P0418, P0440, P0442, P0443, P0446, P0449, P1106, P1107, P1112, P1114, P1115, P1121, P1122, P1415, and P1416 are not set.
^ The Exhaust Gas Recirculation (EGR) flow diagnostic is not active.
^ The Secondary Air Injection (AIR) diagnostic is not active.
^ The catalyst diagnostic is not active.
^ The Closed Loop fuel is enabled.
^ No injectors are disabled.
^ The system voltage is between 9-18 volts.
^ The Air/Fuel ratio is between 14.5-14.8.
^ The Throttle Position (TP) is between 3-25 percent.
^ The above conditions exist for 3 seconds.
CONDITIONS FOR SETTING THE DTC
^ The HO2S signal voltage remains below 75 mV (0.075 V) in Closed Loop mode.
OR
^ The HO2S signal voltage remains below 575 mV (0.575 V) during Power Enrichment (PE) mode.
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
NOTE: Refer to Heated Oxygen Sensor (HO2S) Wire Repair Notice in Service Precautions.
Check for the following conditions:
^ HO2S wire routing-The sensor wiring may be routed incorrectly and contacting the exhaust system.
^ Fuel pressure-Fuel pressure that is too low will cause a lean condition. The PCM will compensate for some decrease. However, if fuel pressure is low enough, the DTC may set.
^ Fuel injectors-If the fuel injectors deliver improper fuel volume at the specified pressure, the DTC may set. Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2. Component Tests and General Diagnostics Component Tests and General Diagnostics
^ Exhaust leak-Exhaust leaks may cause outside air to be drawn into the exhaust gas stream, and pass the HO2S sensor. This causes the HO2S signal to indicate a false lean condition.
^ AIR system leaks-Check the AIR system hoses, the check valves, and the piping for leaks, poor connections, or signs of damage.
^ Vacuum leaks Check for the following:
- Disconnected or damaged vacuum hoses
- Vacuum leaks at the throttle body, EGR valve, Evaporative Emission (EVAP) purge solenoid, and intake manifold
^ Fuel contamination-Water, even in small amounts, can be delivered to the fuel injectors. The water can cause a lean exhaust. Also, excessive alcohol in the fuel can cause a lean condition.
^ Check with the customer to verify the conditions under which the DTC set. Check to see if the vehicle ran out of fuel.
If none of the above conditions are present, replace the HO2S sensor. Refer to Heated Oxygen Sensor (HO2S) Replacement Bank 1 Sensor 1 and Heated Oxygen Sensor (HO2S) Replacement Bank 1 Sensor 2.
Review the front and rear long term fuel trim values on the scan tool fail records data. If both banks were lean, check for a condition that would cause a lean engine operation. If only the rear bank was lean, the lean condition is isolated to that bank, such as an intermittent short to ground on the signal circuit.
If the condition is not present, check with the customer about the type of fuel used, for example, over 10 percent ethanol fuel. Recommend using fuels of 10 percent or less ethanol.
If the condition is intermittent, refer to Intermittent Conditions. Intermittent Conditions
TEST DESCRIPTION
Steps 1-8:
The numbers below refer to the step numbers on the diagnostic table.
2. Verifies whether or not the HO2S sensor voltage is switching from below 300 mV to above 600 mV, or remaining below 300 mV.
4. Verifies the bias voltage from the PCM and the condition of the circuit wiring. With the sensor disconnected, the scan tool should display a bias voltage near 450 mV.