P0031
DTC P0031, P0032, P0037, or P0038
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.
DTC Descriptors
DTC P0031
- HO2S Heater Control Circuit Low Voltage Sensor 1
DTC P0032
- HO2S Heater Control Circuit High Voltage Sensor 1
DTC P0037
- HO2S Heater Control Circuit Low Voltage Sensor 2
DTC P0038
- HO2S Heater Control Circuit High Voltage Sensor 2
Diagnostic Fault Information
Circuit Description
The heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. A heating element inside the HO2S minimizes the time required for the sensor to reach operating temperature. Voltage is provided to the heater by the ignition 1 voltage circuit through a fuse. Ground is provided to the heater on the low control circuit by a low side driver within the control module.
The HO2S utilizes the following circuits:
* A signal circuit
* A low reference circuit
* An ignition 1 voltage circuit
* A heater control circuit
* An oxygen sensor dedicated control module ground circuit
Conditions for Running the DTC
* The ignition voltage is between 10.5-16 volts.
* The engine has been operating for at least 10 seconds.
* The heater control circuit duty cycle is greater than 50 percent.
* The DTCs run continuously when the above conditions are met.
Conditions for Setting the DTC
P0031
When the HO2S 1 heater is commanded ON, the heater circuit current is less than 0.8 amps for greater than 10 seconds.
P0032
When the HO2S 1 heater is commanded OFF, the heater circuit current is greater than 10 amps for greater than 10 seconds.
P0037
When the HO2S 2 heater is commanded ON, the heater circuit current is less than 0.3 amps for greater than 0.5 seconds.
P0038
When the HO2S 2 heater is commanded OFF, the heater circuit current is greater than 2 amps for greater than 2 seconds.
Action Taken When the DTC Sets
DTCs P0031, P0032, P0037, and P0038 are Type A DTCs.
Conditions for Clearing the MIL/DTC
DTCs P0031, P0032, P0037, and P0038 are Type A DTCs.
Diagnostic Aids
The HO2S Heater diagnostic can be monitored on the scan tool under the I/M System Information selection of System Information. When the HO2S Heater test displays a YES status, indicating that the oxygen sensor heater diagnostic is completed, inspect for a DTC P0031, P0032, P0037, or P0038. If there is no DTC displayed the HO2S heater diagnostic has run and passed, indicating that no malfunction was present this time. The DTCs MUST be cleared in order to view the Current Status of the system diagnostics being performed. The I/M System Information tests only indicate that the test has run, not whether the test passed or failed.
Reference Information
Schematic Reference
Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
Note: It may take up to 8 minutes for the DTC to set.
1. Engine at normal operating temperature, operate the engine above 1,200 RPM for 30 seconds and then allow the engine to idle. DTC P0031, P0032, P0037, or P0038 should not set.
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.
2. Ignition ON, verify that a test lamp illuminates between the ignition 1 voltage circuit terminal 2 and ground.
• If the test lamp does not illuminate, test the ignition voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition voltage circuit fuse is open, test all components connected to the ignition voltage circuit and replace as necessary.
3. Ignition OFF, connect a test lamp between the control circuit terminal 1 and B+.
4. Engine running for 1 minute, observe the test lamp. The test lamp should flash ON and OFF during the first 30 seconds of engine run time.
• If the test lamp is always OFF, test the heater control circuit for a for an open/high resistance, or a short to voltage. If the circuit tests normal, replace the PCM.
• If the test lamp is always ON, test the heater control circuit for a short to ground. If the circuit tests normal, replace the PCM.
5. If all circuits test normal, test or replace the HO2S.
Component Testing
1. Ignition OFF, disconnect the harness connector at the appropriate HO2S.
2. Test between the ignition voltage terminal 1 and the heater control terminal 2 for the value specified below:
* HO2S 1-1.8 to 3.4 ohm at 20°C (68°F)
* HO2S 2-11 to 16 ohm at 20°C (68°F)
• If not within the specified range, replace the HO2S sensor.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Heated Oxygen Sensor Replacement - Sensor 1 (Heated Oxygen Sensor Replacement - Sensor 1)
* Heated Oxygen Sensor Replacement - Sensor 2 (Heated Oxygen Sensor Replacement - Sensor 2)
* Control Module References (Programming and Relearning) for control module replacement, setup, and programming