For 1990-2009 cars

### 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 P0030: HO2S Heater Control Circuit Bank 1 Sensor 1
DTC P0031: HO2S Heater Control Circuit Low Voltage Bank 1 Sensor 1
DTC P0032: HO2S Heater Control Circuit High Voltage Bank 1 Sensor 1
DTC P0036: HO2S Heater Control Circuit Bank 1 Sensor 2
DTC P0037: HO2S Heater Control Circuit Low Voltage Bank 1 Sensor 2
DTC P0038: HO2S Heater Control Circuit High Voltage Bank 1 Sensor 2

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Ignition Voltage | P0030, P0031, P0036, P0037 | P0030, P0036 | -- | --
HO2S Heater Control Sensor 1 | P0031 | P0030 | P0032 | --
HO2S Heater Control Sensor 2 | P0037 | P0036 | P0038 | --

### 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 voltage circuit

• | A heater control circuit

### Conditions for Running the DTC

#### P0030, P0031, P0032

• | The engine is running

• | The ignition voltage is between 10-16 volts.

• | The DTCs run continuously once the above conditions are met.

#### P0036, P0037, P0038

• | The ignition voltage is between 10-18 volts.

• | The engine speed is greater than 80 RPM.

• | The HO2S heater is commanded ON and OFF at least once during the ignition cycle.

• | The secondary HO2S is at operating temperature.

• | The DTCs run continuously once the above conditions are met.

### Conditions for Setting the DTC

#### P0030 and P0036

The ECM detects an open in the heater circuits of the HO2S when the heater is commanded OFF.

#### P0031 and P0037

The ECM detects a ground in the heater circuits of the HO2S when the heater is commanded OFF.

#### P0032 and P0038

The ECM detects a short to voltage in the heater circuits of the HO2S when the heater is commanded ON.

### Action Taken When the DTC Sets

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

### Conditions for Clearing the MIL/DTC

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

### Diagnostic Aids

• | If the condition is intermittent, move the related harnesses and connectors, with the engine operating, while monitoring the circuit status for the component with a scan tool. The circuit status parameter changes from OK or Indeterminate to Fault if there is a condition with the circuit or a connection. The ODM information is in the output driver module (ODM) data list.

• | An open fuse in the HO2S heater circuit may be caused by the heater element in one of the sensors. The condition may not be present until the sensor operates for a period of time. If no fault is present in the heater circuit, monitor the amperage of each heater using the DMM to determine if one of the heater elements is the cause of the open fuse. Inspect the sensor pigtail or the harness for contacting the exhaust system.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Engine Control Module Description

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Engine running at operating temperature for at least 30 seconds, observe the DTC information with a scan tool. DTCs P0030, P0031, P0032, P0036, P0037, and 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 heated oxygen sensor (HO2S).
2. Ignition ON, verify a test lamp illuminates between the ignition 1 voltage circuit terminal 2 and ground.

Important: The ignition 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 circuit.

⇒ | If the test lamp is always OFF, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test all the components connected to the ignition 1 voltage circuit and replace as necessary.

3. Ignition OFF, connect a test lamp between the heater control circuit terminal 4 and 12 volts. The test lamp should not illuminate.

⇒ | If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM.

Important: The control circuit for the HO2S heater is pulled-up to voltage within the ECM, 2-3 volts on the control circuit is normal.

4. Engine running, verify the test lamp illuminates or flashes.

⇒ | 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.

5. If all circuits test normal, test or replace the HO2S sensor.

### Component Testing

1. Ignition OFF, disconnect the harness connector at the heated oxygen sensor (HO2S) sensor.
2. Test for 3-35 ohms of resistance between the ignition 1 voltage terminal 2 and the control terminal 4.

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor 1 Replacement

• | Heated Oxygen Sensor 2 Replacement

• | Control Module References for engine control module replacement, setup, and programming