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	Open/High Resistance	Short to Voltage	Signal Performance
Ignition 1 Voltage	--	P0031, P0037	--	--
HO2S 1 Heater Control	P0031	P0031	P0032	P0031
HO2S 2 Heater Control	P0037	P0037	P0038	P0037
PCM HO2S 1 Ground	--	P0031	--	--
PCM HO2S 2 Ground	--	P0037	--	--

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:

Conditions for Running the DTC

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 10 seconds.

P0038

When the HO2S 2 heater is commanded OFF, the heater circuit current is greater than 2 amps for greater than 10 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, check 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. Do not forget that 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

Connector End View Reference

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Important: 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 ground and the ignition 1 voltage circuit terminal as listed below:

•	HO2S 1 ignition 1 voltage circuit terminal 2

•	HO2S 2 ignition 1 voltage circuit terminal 1

⇒	If the test lamp does not illuminate, test the ignition 1 voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition 1 voltage circuit fuse is open, test all components connected to the ignition 1 voltage circuit and replace as necessary.

3. Ignition OFF, connect the harness connector of the HO2S.

Important: The following test must be performed with both the HO2S sensor and the control module connected and operating as normal.

4. Ignition ON, verify a test lamp illuminates between ground and the control module heater control circuit terminal as listed:

•	HO2S 1 heater control circuit PCM terminal X2-5

•	HO2S 2 heater control circuit PCM terminal X2-29

⇒	If the test lamp does not illuminate, test the heater control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the HO2S sensor.

Important: 

•	The following test must be performed with both the HO2S sensor and the control module connected and operating as normal.

•	The test lamp must still be connected to ground and the heater control circuit at the control module.

5. Start and idle the engine for one minute while observing the test lamp. The test lamp should flash ON and OFF during the first 30 seconds of the engine running.

⇒	If the test lamp is always ON, test for an open/high resistance in the PCM oxygen sensor ground circuit as listed:

•	HO2S 1 ground circuit PCM terminal X2-7

•	HO2S 2 heater control circuit PCM terminal X2-6

6. If all circuits test normal, test or replace the PCM.

Component Testing

1. Ignition OFF, disconnect the harness connector at the HO2S.
2. Test for the correct electrical resistance between the ignition 1 voltage circuit terminal and the heater control circuit terminal as listed below:

•	HO2S 1 ignition 1 voltage circuit terminal 2 and the control circuit terminal 1--1.8 to 3.4 ohms at 20°C (68°F)

•	HO2S 2 ignition 1 voltage circuit terminal 1 and the control circuit terminal 2--11 to 16 ohms at 20°C (68°F)

⇒	If not within the specified range, replace the HO2S sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.