P0131
Heated Oxygen Sensor (HO2S) Circuit Low Voltage Sensor 1:
Heated Oxygen Sensor (HO2S) Circuit Low Voltage Sensor 1 (continued):
Heated Oxygen Sensor (HO2S) Circuit Sensor 1:
Circuit Description
The Heated Oxygen Sensor (HO2S) produces a voltage that varies between 100mV and 900mV under normal operating conditions. The Powertrain Control Module (PCM) monitors this voltage and determines if the exhaust is lean or rich. If the voltage input at the PCM is about 100mV the exhaust is lean, and if the voltage input is about 900mV the exhaust is rich. 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
^ Vehicle speed above 32 km/h (20 mph) for 20 seconds.
^ Barometric pressure greater than 75 kPa.
^ Intake air temperature is between -10°C (14°F) and 50°C (122°F).
^ Fuel tank level greater than 25%.
^ Closed loop.
Conditions for Setting the DTC
^ Maximum voltage is less than 300mV
Action Taken When the DTC Sets
^ The Malfunction Indicator Lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.
^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer.
Conditions for Clearing the MIL/DTC
^ The MIL will turn "OFF" after three consecutively passing cycles without a fault present.
^ A History DTC will clear after 40 consecutive warm-up cycles without a fault.
^ DTC(s) can be cleared by using a scan tool or by disconnecting the PCM battery feed.
Diagnostic Aids
Check for the following conditions:
^ If DTC's other than Fuel Trim (P0171, P0172), Misfire (P0300 to P0304), Exhaust Gas Recirculation (EGR) (P0400) and HO2S 1 (P0131 to P0134) are set, diagnose those DTC's first.
^ Heated oxygen sensor wiring. The sensor pigtail may be mis-positioned and contacting the exhaust system.
^ Poor PCM to engine grounds.
^ Fuel Pressure. A condition which causes a lean exhaust can cause DTC P0131 to set. The system will go lean if pressure is too low. The PCM can compensate for some decrease. However, if fuel pressure is too low, a DTC P0131 may be set. Refer to Fuel System Diagnosis.
^ Lean Injector(s)
^ Vacuum leaks. Check for disconnected or damaged vacuum hoses and for vacuum leaks at the intake manifold, throttle body, EGR system, and crankcase ventilation system.
^ Exhaust leaks. An exhaust leak may cause outside air to be pulled into the exhaust gas stream past the HO2S, causing the DTC P0131 to set. Check for exhaust leaks near the HO2S.
^ 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 Fuel System Diagnosis for procedure to check for fuel contamination.
If DTC P0131 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
If any wiring repairs need to be made, Refer to Repair Procedures in Diagrams.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
1. The Powertrain OBD system check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
3. Determines if fault is present, vehicle must be at operating temperature.
4. Review Freeze Frame data to determine when the DTC set. Always record this information.
5. Checks for an open in the HO2S 1 ground circuit.
6. Checks for an open or short in the HO2S 1 signal circuit.