Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptors
DTC P0031: HO2S Heater Control Circuit Low Voltage Sensor 1DTC 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 | -- |
HO2S 2 Heater Control | P0037 | P0037 | P0038 | -- |
* Engine cranks but does not run and the fuse for the ignition circuit opens. | ||||
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 control module monitors the current draw of the heater to determine if a failure is present.
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 DTCs run continuously when the above condition is met. |
Conditions for Setting the DTC
P0031 and P0037
The ECM detects that the HO2S heater pulse width modulation (PWM) is greater than 98 percent .
P0032
The ECM detects that the HO2S heater pulse width modulation (PWM) is less than 39 percent .
P0038
The ECM detects that the HO2S heater pulse width modulation (PWM) is greater than 99 percent .
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
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
- Engine running at normal operating temperature, operate the engine above 1,200 RPM for 30 seconds and then allow the engine to idle. DTCs P0031, P0032, P0037, or P0038 should not set.
- 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.
Important: It may take up to 8 minutes for the DTC to set.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the appropriate HO2S.
- Ignition ON, verify that a test lamp illuminates between the ignition 1 voltage circuit terminal 4 and ground.
- Ignition OFF, connect a test lamp between the control circuit terminal 2 and B+. The test lamp should not illuminate.
- If all circuits test normal, test or replace the HO2S sensor.
Important: The ignition 1 voltage circuit supplies voltage to other components. Make sure you test all circuits for a short to ground or test all components for being shorted that share the ignition 1 voltage circuit.
| ⇒ | 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. |
| ⇒ | If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM. |
| ⇒ | If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM. |
Component Testing
- Ignition OFF, disconnect the harness connector at the HO2S.
- Test for 4-6 ohms of resistance between the ignition 1 voltage terminal 4 and the control terminal 2.
| ⇒ | If not within the specified range, replace the HO2S sensor. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for ECM replacement, setup, and programming |
