P0031

DTC P0031, P0032, P0037, or P0038

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

Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.






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

Conditions for Running the DTC

* The engine is running.
* The ignition 1 voltage is between 7.5-16 volts.
* The DTC runs continuously when the above conditions are met.

Conditions for Setting the DTC

The ECM detects an open, short to ground, or voltage on the control circuit of the H02S.

Action Taken When the DTC Sets

DTC P0031, P0032, P0037, and P0038 are Type A DTCs.

Conditions for Clearing the MIL/DTC

DTC P0031, P0032, P0037, and P0038 are Type A DTCs.

Reference Information

Schematic Reference

Engine Controls Schematics Electrical Diagrams

Connector End View Reference
* Engine Control Module (ECM) Connector End Views Engine Control Module (ECM) Connector End Views
* Engine Controls Connector End Views Engine Controls Connector End 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

Diagnostic Trouble Code (DTC) Type Definitions Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference
* Scan Tool Data List Scan Tool Data List
* Scan Tool Data Definitions Scan Tool Data Definitions
* Scan Tool Output Controls Scan Tool Output Controls

Circuit/System Verification

Important: It may take up to 8 minutes for the DTC to set.


1. With the 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. If the vehicle passes the Circuit/System Verification Test, then operate the vehicle within the conditions for running the DTC. 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 of the H02S.

Important: The test lamp is used to load the circuit and may not illuminate.


2. Connect a test lamp between the ignition 1 voltage circuit of the H02S heater and the negative terminal of the battery.
3. Ignition ON, test for less than 0.1 volt between the ignition 1 voltage circuit of the H02S heater and the positive terminal of the battery.

• If greater than 0.1 volt, test the ignition 1 voltage circuit of the H02S heater for a short to ground or an open/high resistance. If the circuit/connections test normal, replace the H02S sensor.

4. Ignition OFF, connect a test lamp between the control circuit of the H02S heater and the positive terminal of the battery.

• If test lamp illuminates, test the control circuit of the H02S heater for a short to ground. If the circuit/connections test normal, replace the ECM.

5. Ignition ON, test for less than 0.3 volt between the control circuit of the H02S heater and the negative terminal of the battery.

• If greater than 0.3 volt, test the control circuit of the H02S heater for a short to voltage or an open/high resistance. If the circuit/connections test normal, replace the ECM.

6. If all circuits/connections test normal, test or replace the H02S sensor.

Component Testing

1. Ignition OFF, disconnect the harness connector of the heated oxygen sensor (H02S) sensor.
2. Measure for 3-35 ohms of resistance between the ignition 1 voltage circuit terminal and the control circuit terminal of the H02S heater.

• If the resistance is out of the specified range, replace the H02S sensor.

Repair Instructions

Important: Always perform the Diagnostic Repair Verification Diagnostic Repair Verification after completing the diagnostic procedure.


* Heated Oxygen Sensor Replacement - Position 1 Heated Oxygen Sensor Replacement - Position 1
* Heated Oxygen Sensor Replacement - Position 2 Heated Oxygen Sensor Replacement - Position 2
* Control Module References Control Module References for engine control module replacement, setup, and programming