P0038
DTC P0031, P0032, 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 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 battery is between 10.5-16 volts.
* The engine has been operating for at least 10 seconds.
* The heater control circuit duty cycle is more than 50 percent.
* No current misfire is detected.
* The DTCs run continuously when the above conditions are met.
Conditions for Setting the DTC
* The HO2S heater is commanded ON for more than 0.2 seconds.
* The HO2S heater current is less than 0.8 amps.
* The condition exists for more than 10 seconds.
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.
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 in the Last Test Failed screen of the scan tool. 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. The Last Test Failed screen must be checked for related DTCs in order to determine the outcome of the diagnostic test involved. For additional information on check mode operation refer to Powertrain Control Module Diagnosis.
Reference Information
Schematic Reference
Engine Controls Schematics (Electrical Diagrams)
Connector End View Reference
* Powertrain Control Module Connector End Views (Powertrain Control Module Connector End Views)
* Engine Controls Connector End Views (Engine Controls Connector End 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
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 C2-5
* HO2S 2 heater control circuit PCM terminal C2-29
• 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 C2-7
* HO2S 2 heater control circuit PCM terminal C2-6
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 (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 ECM replacement, setup, and programming