Diagnostic Instructions

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	Short to Ground	High Resistance	Open	Short to Voltage	Signal Performance
HO2S Heater Voltage Supply	Opens fuse	P0031, P0037, P0135, P0141,	P0031, P0037, P0135, P0141	--	P0135, P0141
HO2S Heater Low Control	P0031, P0037,	P0031, P0037, P0135, P0141	P0031, P0037, P0135, P0141	P0032, P0038, P0135, P0141	P0135, P0141

Typical Scan Tool Data

HO2S Heater

Circuit	Normal Range	Short to Ground	Open	Short to Voltage
HO2S Heater Low Control	1-2 A	0 A	0 A	0 A
HO2S Heater Voltage Supply	1-2 A	0 A	0 A	1-2 A

Circuit/System Description

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 an ignition voltage circuit through a fuse. With the engine running, ground is provided to the heater by the HO2S heater low control circuit, through a low side driver within the engine control module (ECM). The ECM commands the heater ON or OFF to maintain a specific HO2S operating temperature range.

The ECM monitors the voltage on the HO2S heater low control circuit for heater fault diagnosis. If the ECM detects that the HO2S heater low control circuit voltage is not within a specified range, DTC P0031 or P0032 sets for HO2S 1, or DTC P0037 or P0038 sets for HO2S 2.

Conditions for Running the DTC

Conditions for Setting the DTC

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Electrical Information Reference

Scan Tool Reference

Scan Tool Data List

Circuit/System Verification

Circuit/System Testing

1. Disconnect the sensor.
2. Ignition ON, connect a test lamp between the HO2S heater voltage supply circuit terminal D and ground. The lamp should illuminate.

⇒	If the lamp does not illuminate, test the voltage supply circuit for open/high resistance or a short to ground.

⇒	If the circuit tests normal and its fuse is open, replace the HO2S.

3. Ignition OFF, connect a test lamp between the HO2S low control circuit terminal C and battery voltage. The lamp should not illuminate.

⇒	If the lamp illuminates, test the low control circuit for a short to ground. If the circuit tests normal, replace the ECM.

4. Engine running, leave the test lamp connected from the previous step. The lamp should flash or be ON steady.

⇒	If the test lamp is not ON steady or flashing, then test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

Important: 

•	The output driver should detect a short to voltage and turn OFF. If a resistance fault is present, the driver will remain ON and the scan tool will display more than 0 amp. Less than 10 ohms of resistance may set a DTC.

•	Performing this test may set additional DTCs.

5. Ignition OFF, install a 30A fused jumper wire from the heater supply circuit terminal D to the heater control circuit terminal C.
6. Engine running, observe the scan tool that the Heater parameter indicates 0.0A.

⇒	If more than the specified value, test the heater voltage supply and controls circuits for resistance greater than 3 ohms. If the circuits test normal, replace the ECM.

7. If the ECM and all circuits test normal, replace the HO2S sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.