P0131
DTC P0131
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
DTC Descriptors
DTC P0131
- HO2S Circuit Low Voltage Sensor 1
Diagnostic Fault Information
Circuit Description
The wide band heated oxygen sensor (HO2S) measures the amount of oxygen in the exhaust system and provides more information than the switching style HO2S. The wide band sensor consists of an oxygen sensing cell, an oxygen pumping cell, and a heater. The exhaust gas sample passes through a diffusion gap between the sensing cell and the pumping cell. The engine control module (ECM) supplies a voltage to the HO2S and uses this voltage as a reference to the amount of oxygen in the exhaust system. An electronic circuit within the ECM controls the pump current through the oxygen pumping cell in order to maintain a constant voltage in the oxygen sensing cell. The ECM monitors the voltage variation in the sensing cell and attempts to keep the voltage constant by increasing or decreasing the amount of current flow, or oxygen ion flow, to the pumping cell. By measuring the amount of current required to maintain the voltage in the sensing cell, the ECM can determine the concentration of oxygen in the exhaust. The HO2S voltage is displayed as a lambda value. A lambda value of 1 is equal to a stoichiometric air fuel ratio of 14.7:1. Under normal operating conditions, the lambda value will remain around 1. When the fuel system is lean, the oxygen level will be high and the lambda signal will be high or more than 1. When the fuel system is rich, the oxygen level will be low, and the lambda signal will be low or less than 1. The ECM uses this information to maintain the correct air/fuel ratio.
Conditions for Running the DTC
* The engine is operating.
* The ignition 1 voltage is between 11-18 volts.
* DTC P0131 runs continuously once the above conditions are met for greater than 2 seconds.
Conditions for Setting the DTC
* The internal ECM HO2S voltage is less than a threshold.
* The above condition exists for greater than 4 seconds.
Action Taken when the DTC Sets
DTC P0131 is a Type B DTC.
Conditions for Clearing the MIL/DTC
DTC P0131 is a Type B DTC.
Reference Information
Schematic Reference
Engine Controls Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Diagnostic Aids
The following table illustrates the ECM connector locations:
* The front wide band sensor does not toggle or switch like a switching HO2S. The front HO2S signal will be relatively stable for an idling engine.
* The following table illustrates the typical voltages for the HO2S circuits:
Circuit/System Verification
Important: Inspect the heated oxygen sensor (HO2S) for being secure before proceeding with this DTC. A sensor that is loose could cause this DTC to set.
1. Engine idling at operating temperature. Observe the scan tool Loop Status Sen 1 parameter. Verify the parameter displays Closed Loop.
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 are captured in the Freeze Frame/Failure Records Data List.
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the HO2S 1.
2. Ignition ON, test for 2.5-3.5 volts between the high signal circuit terminal 1 and ground.
• If less than the specified range, test the high signal circuit for a short to ground, or an open/high resistance. If the circuit tests normal, replace the ECM.
• If greater than the specified range, test the high signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
3. Test for 2-3 volts between the low signal circuit terminal 5 and ground
• If less than the specified range, test the low signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
• If greater than the specified range, test the low signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
Important: The input pumping current circuit and the pump current circuit are connected internally within the ECM. If there is a condition with one of the circuits, the other circuit will be affected.
4. Connect a test lamp between the input pump current circuit terminal 6 and B+. Verify the test lamp does not illuminate.
• If the test lamp illuminates, test the input pump circuit and pump current circuit for a short to ground. If the circuit tests 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 (Fuel Injector Balance Test With Special Tool) or Fuel Injector Balance Test with Tech 2 (Fuel Injector Balance Test With Tech 2).
* Incorrect 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 (Without Special Tool))Alcohol/Contaminants-in-Fuel Diagnosis (w/ 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 test normal, replace the HO2S 1.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Heated Oxygen Sensor 1 Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for engine control module replacement, setup, and programming