P0131
DTC P0131 or P0151
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptors
DTC P0131
- HO2S Circuit Low Voltage Bank 1 Sensor 1
DTC P0151
- HO2S Circuit Low Voltage Bank 2 Sensor 1
Diagnostic Fault Information
Typical Scan Tool Data
Circuit Description
The heated oxygen sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the control module operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the HO2S with a reference, or bias voltage of about 450 mV. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,000 mV. This voltage will fluctuate above and below the bias voltage. Once sufficient HO2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.
The heating elements inside each HO2S heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the control module to calculate the air-to-fuel ratio sooner.
Conditions for Running the DTC
* DTC P0116, P0117, P0118, P0119, P0201, P0202, P0203, P0204, P0205, P0206 P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, or P0277 is not set.
* The ignition voltage is greater than 10.5 volts.
* The engine is operating for greater than 1 second.
* The engine coolant temperature (ECT) during the previous ignition cycle was greater than 60°C (140°F).
* The ECT at startup is less than 40°C (104°F).
* The HO2S heater is active for greater than 8 seconds.
* The calculated exhaust temperature is less than 800°C (1,472°F).
* DTC P0131 and P0151 run continuously once the conditions above exist.
Conditions for Setting the DTC
* The ECM detects that the HO2S 1 voltage is less than 60 mV while the corresponding HO2S 2 voltage is greater than 500 mV.
* The ECM detects that the HO2S 1 voltage is less than 60 mV after a cold start with the engine coolant temperature (ECT) less than 40°C (104°F).
* The ECM detects either condition for greater than 1 second.
Action Taken when the DTC Sets
DTCs P0131 and P0151 are Type B DTCs.
Conditions for Clearing the MIL/DTC
DTCs P0131 and P0151 are Type B DTCs.
Circuit/System Verification
1. Engine idling, observe the appropriate scan tool HO2S voltage parameter. The voltage should fluctuate above and below the range of 350-550 mV.
2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the appropriate HO2S sensor.
2. Ignition ON, verify the scan tool HO2S voltage parameter is between 350-500 mV.
^ If less than the specified value, test the signal circuit for a short to ground. If the circuit/connections test normal, replace the ECM.
^ If greater than the specified value, test the signal circuit for a short to voltage. If the circuit/connections test normal, replace the ECM.
3. Install a 3A fused jumper wire between the signal circuit terminal B and ground. Verify the scan tool HO2S voltage parameter is less than 60 mV.
^ If greater than the specified value, test the signal circuit for an open/high resistance. If the circuit/connections test normal, replace the ECM.
4. Connect a 3A fused jumper wire between the signal circuit terminal B and the low reference circuit terminal A. Verify the scan tool HO2S voltage parameter is less than 60 mV.
^ If greater than the specified value, test the low reference circuit for an open/high resistance or for a short to voltage. If the circuit/connections test normal, replace the ECM.
5. Verify that the following conditions do not exist:
* Lean fuel injectors-Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2. Fuel Injector Balance Test With Special Tool Fuel Injector Balance Test With Tech 2
* Low fuel system pressure-Refer to Fuel System Diagnosis. Component Tests and General Diagnostics
* Fuel that is contaminated-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) Alcohol/Contaminants-in-Fuel Diagnosis (w/ Special Tool). Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) Alcohol/Contaminants-In-Fuel Diagnosis (With Special Tool)
* Exhaust leaks near the HO2S
* Engine vacuum leaks
^ If you find any of the above conditions, repair as necessary.
6. If all circuits/connections test normal, replace the HO2S sensor.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Heated Oxygen Sensor Replacement - Bank 1 Sensor 1
* Heated Oxygen Sensor Replacement - Bank 2 Sensor 1.