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 P0036: HO2S Heater Control Circuit Sensor 2
DTC P0037: HO2S Heater Control Circuit Low Voltage Sensor 2
DTC P0038: HO2S Heater Control Circuit High Voltage Sensor 2
DTC P0141: HO2S Heater Performance Sensor 2

### Diagnostic Fault Information

Circuit | Short to Ground | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
HO2S 2 Heater Voltage Supply | Opens fuse | P0036, P0037, P0141 | -- | P0141
HO2S 2 Heater Low Control | P0036, P0037, | P0036, P0037, P0141 | P0036, P0038, P0141 | P0141
HO2S 2 Signal High | P0137 | -- | P0138 | --
HO2S 2 Reference Ground | -- | -- | -- | --

### Circuit/System Description

Heated oxygen sensors (HO2S) are used for fuel control and post-catalyst monitoring. The HO2S 2 compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S 2 must reach operating temperature to provide an accurate voltage signal. A heating element inside the HO2S 2 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 2 heater low control circuit, through a low side driver within the Engine Control Module (ECM). The ECM uses pulse-width modulation (PWM) to control the HO2S 2 heater operation to maintain a specific HO2S 2 operating temperature range.

#### P0036

The ECM monitors the voltage on the HO2S 2 heater low control circuit for heater fault diagnosis. If the ECM detects that the HO2S 2 heater low control circuit voltage is not within a specified range, DTC P0036 sets.

#### P0037

The ECM monitors the voltage on the HO2S 2 heater low control circuit for heater fault diagnosis. If the ECM detects that the HO2S 2 heater low control circuit voltage is below a specified range, DTC P0037 sets.

#### P0038

The ECM monitors the voltage on the HO2S 2 heater low control circuit for heater fault diagnosis. If the ECM detects that the HO2S 2 heater low control circuit voltage is above a specified range, DTC P0038 sets.

#### P0141

If the ECM detects that the heater current is not within the expected range, DTC P0141 sets.

### Conditions for Running the DTC

#### P0036, P0037, and P0038

• | The Ignition 1 Signal parameter is between 10-18 volts.

• | The engine speed is more than 80 RPM.

• | DTC P0036, P0037, and P0038 run continuously when the above conditions are met for 1 second.

#### P0141 Heater Resistance Test

• | DTCs P0036, P0037, P0038, P0121, P0122, P0123, P0137, P0138, P0140, P0221, P0222, P0223, P0335, P0336, P0338, P2232, P2271, P2271 are not set.

• | The Ignition 1 Signal parameter is between 10-18 volts.

• | The modeled exhaust gas temperature is between 360-500°C (680-932°F).

• | The engine off soak time is greater than 120 seconds.

• | The engine is not in decel fuel cut-off.

• | The intake air temperature (IAT) is greater than -30°C (-22°F).

• | DTC P0141 runs continuously.

### Conditions for Setting the DTC

#### P0036, P0037, and P0038

• | The ECM detects that the difference between the expected and the actual HO2S 2 heater low control circuit voltage is more than a calibrated value.

• | DTCs P0036, P0037, and P0038 set when the above condition is met for 4 seconds continuously, or for 50 seconds cumulatively.

#### P0141 Heater Resistance Test

• | The ECM detects that the HO2S 2 heater current is more than 2.5 amps or less than 0.25 amp.

• | DTC P0141 sets within 30 seconds during the heater current test when the above condition is met.

### Action Taken When the DTC Sets

DTC P0036, P0037, P0038, P0141 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTC P0036, P0037, P0038, P0141 are Type B DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

• | Heated Oxygen Sensor 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. Clear the DTCs with a scan tool.
2. Operate the vehicle within the conditions for running and setting the DTC. The DTC should not set.
3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

### Circuit/System Testing

Note: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

1. Ignition OFF, disconnect the harness connector at the B52B HO2S 2.
2. Ignition ON, verify that a test lamp illuminates between the B52B HO2S 2 heater voltage supply circuit terminal 1 and ground.

⇒ | If the test lamp does not illuminate, test the B52B HO2S 2 heater voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all components connected to the fuse and replace as necessary.

3. Ignition ON, verify that a test lamp does not illuminate between the B52B HO2S 2 heater low control circuit terminal 2 and the B52B HO2S 2 heater voltage supply circuit terminal 1.

⇒ | If the test lamp illuminates, test the B52B HO2S 2 heater low control circuit for a short to ground. If the circuit tests normal, replace the K20 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, test the B52B HO2S 2 heater low control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K20 ECM.

5. If the K20 ECM and all circuits test normal, replace the B52B HO2S 2.

### Repair Instructions

Caution: Refer to Heated Oxygen Sensor Resistance Learn Reset Caution in the Preface section.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor 1 Replacement

• | Heated Oxygen Sensor 2 Replacement

• | Control Module References for ECM replacement, setup, and programming