GM Service Manual Online
For 1990-2009 cars only

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 P0131: HO2S Circuit Low Voltage Sensor 1

DTC P0132: HO2S Circuit High Voltage Sensor 1

DTC P0137: HO2S Circuit Low Voltage Sensor 2

DTC P0138: HO2S Circuit High Voltage Sensor 2

Diagnostic Fault Information

HO2S Sensor 1

Circuit

Short to Ground

High Resistance

Open

Short to Voltage

Signal Performance

HO2S High Signal

P0131, P0171, P1133, P2A00

P0131, P0133, P0134, P1133, P2A00

P0131, P0133, P0134, P1133, P2A00

P0132, P0134, P0172, P1133, P2A00

P0133, P0134, P1133, P2A00

HO2S Low Signal

P2A00

P0133, P0134, P1133, P2A00

P0133, P0134, P1133, P2A00

P0134, P1133, P2A00

P2A00

HO2S Sensor 2

Circuit

Short to Ground

High Resistance

Open

Short to Voltage

Signal Performance

HO2S High Signal

P0137, P0140, P2270

P0140, P2271

P0140, P2271

P0138, P0140, P2271

P0140, P2271

HO2S Low Signal

--

P0140, P2270, P2271

P0140, P2A01, P2270, P2271

P0138, P0140, P2270, P2271

P2271

Typical Scan Tool Data

HO2S Sensor 1

HO2S Sensor Voltage Circuits

Normal Range

Short to Ground

Open

Short to Voltage

HO2S High Signal

0-1000 mV

0-45 mV

Approximately 450 mV

Approximately 1106 mV

HO2S Low Signal

0-1000 mV

0-1000 mV

0-800 mV

50-1106 mV

HO2S Sensor 2

HO2S Sensor Voltage Circuits

Normal Range

Short to Ground

Open

Short to Voltage

HO2S High Signal

0-1000 mV

0-45 mV

Approximately 450 mV

Approximately 1106 mV

HO2S Low Signal

0-1000 mV

0-1000 mV

400-600 mV

50-1106 mV

Circuit/System Description

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. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The powertrain control module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started, the PCM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.

Conditions for Running the DTC

P0131 and P0137

    • DTCs P0068, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0220, P0442, P0443, P0446, P0449, P0451, P0452, P0453, P0454, P0455, P0496, P1516, P2101, P2119, P2135 are not set.
    • DTCs P0411, P0412, P0418, P2400, P2430-P2433, P2444, where applicable, are not set.
    • The system voltage is between 10-18 volts.
    • The scan tool special functions are not active.
    • The Air Fuel Ratio parameter is between 0.9-1.1.
    • The TP Indicated Angle parameter is between 3-40 percent.
    • The Loop Status parameter is closed.
    • The ECT parameter is less than 131°C (267°F).
    • The traction control is not active.
    • The above conditions have been met for at least 3 seconds.

P0132 and P0138

    • DTCs P0068, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0220, P0442, P0443, P0446, P0449, P0451, P0452, P0453, P0454, P0455, P0496, P1516, P2101, P2119, P2135 are not set.
    • DTCs P0411, P0412, P0418, P2400, P2430-P2433, P2444, where applicable, are not set.
    • The system voltage is between 10-18 volts.
    • The scan tool special functions are not active.
    • The TP Indicated Angle parameter is less than 46 percent.
    • The Air Fuel Ratio parameter is between 0.9-1.1.
    • The above conditions must be met for at least 3 seconds.

Conditions for Setting the DTC

P0131

    • The PCM detects that the HO2S 1 signal voltage is less than 52 mV for more than 26 seconds.
    • This diagnostic runs continuously.

P0132

    • The PCM detects that the HO2S 1 signal voltage is more than 1,050 mV for more than 9 seconds.
    • This diagnostic runs continuously.

P0137

    • The PCM detects that the HO2S 2 signal voltage remains below 52 mV for more than 60 seconds.
    • This diagnostic runs continuously.

P0138

    • The HO2S  2 voltage is more than 1,050  mV for longer than 60 seconds.
    • This diagnostic runs continuously.

Action Taken When the DTC Sets

DTCs P0131, P0132, P0137, and P0138 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0131, P0132, P0137, and P0138 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
    •  Heated Oxygen Sensor Wiring 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. If any HO2S heater DTCs are set, perform those diagnostics first.
  2. Allow the engine to reach operating temperature.
  3. Engine running, observe the affected HO2S parameter with a scan tool.
  4. The pre-catalyst oxygen sensors value should vary from below 200 mV to above 800 mV and respond to fueling changes.
    The post-catalyst oxygen sensors value should change more than 200 mV when the throttle is quickly cycled 3 times from closed to wide open and back to closed after running the engine at 1,500 RPM for 30 seconds.
  5. The affected HO2S may be damaged due to contamination. Prior to replacing the affected HO2S, inspect for the following sources of contamination:
  6. Notice: Refer to Silicon Contamination of Heated Oxygen Sensors Notice in the Preface section.

    • A silicon contaminated HO2S
    • Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Engine oil consumption--Refer to Oil Consumption Diagnosis .
    • Engine coolant consumption--Refer to Loss of Coolant .
  7. 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

Important: All modules must be powered down or misdiagnosis may result.

  1. Ignition OFF, disconnect the scan tool and wait 60 seconds to ensure all modules are powered down.
  2. Ignition OFF, disconnect the harness connector at the appropriate HO2S.
  3. Ignition OFF, measure for less than 5 ohms between the appropriate HO2S low signal circuit terminal A and ground.
  4. If more than the specified range, test the appropriate HO2S low signal circuit for an open/high resistance. If the circuit tests normal, replace the PCM.
  5. Ignition ON, verify the appropriate scan tool HO2S parameter is approximately 450 mV.
  6. If more than the specified value, test the appropriate HO2S high signal circuit for a short to voltage. If the circuit tests normal, replace the PCM.
    If less than the specified value, test the appropriate HO2S high signal circuit for a short to ground. If the circuit tests normal, replace the PCM.
  7. Ignition ON, install a 3A fused jumper wire at the HO2S high signal circuit terminal B. Toggle the jumper wire between the HO2S low signal circuit terminal A and the battery voltage. Verify the appropriate scan tool HO2S parameter toggles between 0 mV and approximately 1,000 mV.
  8. If the appropriate scan tool HO2S parameter does not toggle correctly, test the HO2S high signal circuit for an open/high resistance. If the circuits test normal, replace the PCM.
  9. If all circuits test normal, replace the appropriate HO2S.

Repair Instructions

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

Important: For DTCs P0131 and P0132, in order to ensure that the performance of the catalyst has not been affected by the fault that set this DTC, operate the vehicle within the Conditions for Running and setting DTC P0420, and verify that DTC P0420 runs and passes. Refer to DTC P0420 .

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Heated Oxygen Sensor 1 Replacement
    •  Heated Oxygen Sensor 2 Replacement
    •  Control Module References for replacement, setup, and programming