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 Bank 1 Sensor 1

DTC P0151: HO2S Circuit Low Voltage Bank 2 Sensor 1

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

HO2S Bank 1 Sensor 1 Signal

P0131

P0134, P0135

P0132

P0133, P2096, P2097

HO2S Bank 1 Sensor 2 Signal

P0137

P0140, P013A

P0138

P0140, P013A, P013E

HO2S Bank 2 Sensor 1 Signal

P0151

P0154, P0155

P0152

P0153, P2098, P2099

HO2S Bank 2 Sensor 2 Signal

P0157

P0160, P013C

P0158

P0160, P013C, P014A

HO2S Bank 1 Sensor 1 Low Reference

--

P0134, P0135

--

P0133, P2096, P2097

HO2S Bank 1 Sensor 2 Low Reference

--

P0140, P013A

--

P0140, P013A, P013E

HO2S Bank 2 Sensor 1 Low Reference

--

P0154, P0155

--

P0153, P2098, P2099

HO2S Bank 2 Sensor 2 Low Reference

--

P0160, P013C

--

P0160, P013C, P014A

Typical Scan Tool Data

HO2S 1 or 2

Circuit

Short to Ground

Open

Short to Voltage

Operating Conditions: Engine operating in Closed Loop

Parameter Normal Range: Fluctuates above and below 350-500 mV

Sensor Signal

0-60 mV

445-450 mV

1275 mV

Low Reference

--

445-480 mV

1275 mV

Circuit Description

The heated oxygen sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the control module operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the HO2S with a reference, or bias voltage of about 450 mV. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,000 mV. This voltage will fluctuate above and below the bias voltage. Once sufficient HO2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.

The heating elements inside each HO2S heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the control module to calculate the air-to-fuel ratio sooner.

Conditions for Running the DTC

Condition 1

    • DTC P0201, P0202, P0203, P0204, P0205, P0206 P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, P0277, P2146, P2149, P2152, P2155, P216A, or P216D is not set.
    • The ignition voltage is greater than 10 volts.
    • The engine speed is greater than 240 RPM.
    • The air flow into the engine is greater than 220 grams.
    • The HO2S 1 heater duty cycle is greater than 90 percent for greater than 5 seconds.
    • The evaporative emissions system (EVAP) is not performing an intrusive test.
    • The ECM is not commanding the air/fuel mixture lean.
    • DTC P0131 and P0151 run continuously once the conditions above exist for greater than 5 seconds.

Condition 2

    • DTC P0116, P0117, P0118, P0119, P0201, P0202, P0203, P0204, P0205, P0206 P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, P0277, P2146, P2149, P2152, P2155, P216A, or P216D is not set.
    • The ignition voltage is greater than 10 volts.
    • The engine speed is greater than 240 RPM.
    • The conditions for a cold start are present.
    • The HO2S 1 heater duty cycle is greater than 90 percent for greater than 5 seconds.
    • DTC P0131 and P0151 run continuously once the conditions above exist.

Conditions for Setting the DTC

Condition 1

The ECM detects that an HO2S 1 signal voltage is less than 60 mV while the corresponding HO2S 2 voltage is greater than 500 mV.

Condition 2

The ECM detects that an HO2S 1 signal voltage is less than 60 mV after a cold start.

Action Taken when the DTC Sets

DTCs P0131 and P0151 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0131 and P0151 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

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 idling, observe the appropriate scan tool HO2S 1 voltage parameter. The voltage should fluctuate above and below the range of 350-550 mV.
  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 1.
  2. Ignition ON, verify that the scan tool HO2S 1 voltage parameter is between 350-500 mV.
  3. If less than the specified range, test the signal circuit terminal B for a short to ground. If the circuit/connections test normal, replace the ECM.
    If greater than the specified range, test the signal circuit terminal B for a short to voltage. If the circuit/connections test normal, replace the ECM.
  4. Install a 3 A fused jumper wire between the signal circuit terminal B and ground. Verify the HO2S voltage parameter is less than 60 mV.
  5. If greater than the specified range, test the signal circuit for an open/high resistance. If the circuit/connections test normal, replace the ECM.
  6. Connect a 3 A fused jumper wire between the signal circuit terminal B and the low reference circuit terminal A. Verify the HO2S voltage parameter is less than 60 mV.
  7. If greater than the specified range, test the low reference circuit for an open/high resistance or for a short to voltage. If the circuit/connections test normal, replace the ECM.
  8. Verify that the following conditions do not exist:
  9. • Lean condition.
    • Low fuel system pressure--Refer to Fuel System Diagnosis.
    • Fuel that is contaminated--Refer to Alcohol/Contaminants-in-Fuel Diagnosis.
    • Exhaust leaks near the HO2S.
    • Engine vacuum leaks.
         ⇒If you find any of the above conditions, repair as necessary.
  10. If all circuits/connections test normal, replace the appropriate HO2S 1.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Heated Oxygen Sensor Replacement - Bank 1 Sensor 1
    •  Heated Oxygen Sensor Replacement - Bank 2 Sensor 1
    •  Control Module References for engine control module replacement, setup, and programming