P0031

DTC P0030, P0031, P0032, P0036, P0037, or P0038

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 P0030
- HO2S Heater Control Circuit Sensor 1

DTC P0031
- HO2S Heater Control Circuit Low Voltage Sensor 1

DTC P0032
- HO2S Heater Control Circuit High Voltage Sensor 1

DTC P0036
- HO2S Heater Control Circuit Sensor 2

DTC P0037
- HO2S Heater Control Circuit Low Voltage Sensor 2

DTC P0038
- HO2S Heater Control Circuit High Voltage Sensor 2




Circuit/System Description

The heated oxygen sensor (HO2S) heater reduces the time required for the oxygen sensor (O2S) to reach operating temperature and maintains the operating temperature during extended idle periods. When the ignition is turned to the ON position, ignition voltage is supplied directly to the sensor heater. The engine control module (ECM) controls the heater operation by first modulating the control circuit to ground when the sensors are cold. This prevents the possibility of thermal shock to the sensor, from condensation build-up on the sensor, by controlling the sensors rate of heating. After a predetermined amount of time, the ECM commands the heaters ON continuously. Once the sensor reaches operating temperature, the ECM may modulate the heater control circuit to ground, to maintain a desired temperature.


The ECM controls the heater by grounding the control circuit with a solid state device called a driver. The driver is equipped with a feedback circuit that is pulled-up to voltage. The ECM can determine if the control circuit is open, shorted to ground, or shorted to a voltage by monitoring the feedback voltage.


Diagnostic Fault Information






Conditions for Running the DTC

* The ignition voltage is between 11-18 volts.
* The engine speed is greater than 80 RPM.
* The DTCs run continuously once the above conditions are met for less than 1 second.



Conditions for Setting the DTC


P0030 or P0036
* The ECM detects an open in the heater circuits of the HO2S when the heater is commanded OFF.
* The above condition exists for greater than 4 seconds.



P0031 or P0037
* The ECM detects a ground in the heater circuits of the HO2S when the heater is commanded OFF.
* The above condition exists for greater than 4 seconds.



P0032 or P0038
* The ECM detects a short to voltage in the heater circuits of the HO2S when the heater is commanded ON.
* The above condition exists for greater than 4 seconds.



Action Taken When the DTC Sets

DTCs P0030, P0031, P0032, P0036, P0037, and P0038 are Type B DTCs.


Conditions for Clearing the DTC

DTCs P0030, P0031, P0032, P0036, P0037, and P0038 are Type B DTCs.


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.
* Inspect the sensor pigtail or the harness for contacting the exhaust system.



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


Circuit/System Verification

1. Engine idling at operating temperature for at least 30 seconds. Observe the scan tool DTC information. DTCs P0030, P0031, P0032, P0036, 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 are captured in the Freeze Frame/Failure Records Data List.



Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the appropriate HO2S.
2. Ignition ON, test for B+ between the ignition voltage circuit and ground.

* HO2S 1 terminal 3
* HO2S 2 terminal E


• If less than the specified range, repair the ignition voltage circuit for a short to ground, or an open/high resistance.

3. Test for 4.6-5 volts between the heater control circuit and ground.

* HO2S 1 terminal 4
* HO2S 2 terminal D


• If less than the specified range, test the heater control 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 heater control circuit for a short to voltage. If the circuit tests normal, replace the ECM.

4. Connect a test lamp between the heater control circuit and B+. Engine idling, the test lamp should illuminate, or flash.

* HO2S 1 terminal 4
* HO2S 2 terminal D


• If the test lamp does not illuminate, or flash, replace the ECM.

5. If all circuits test normal, replace the appropriate HO2S.



Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Heated Oxygen Sensor 1 Replacement (Service and Repair)
* Heated Oxygen Sensor 2 Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for engine control module replacement, setup, and programming