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  P0137: HO2S Circuit Low Voltage Bank 1 Sensor 2

DTC P0138: HO2S Circuit High Voltage Bank 1 Sensor 2

DTC P0140: HO2S Circuit Insufficient Activity Bank 1 Sensor 2

DTC P0157: HO2S Circuit Low Voltage Bank 2 Sensor 2

DTC P0158: HO2S Circuit High Voltage Bank 2 Sensor 2

DTC P0160: HO2S Circuit Insufficient Activity Bank 2 Sensor 2

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

P0138

P0140

HO2S Bank 2 Sensor 1 Signal

P0151

P0154, P0155

P0152

P0153, P2098, P2099

HO2S Bank 2 Sensor 2 Signal

P0157

P0160

P0158

P0160

Low Reference

--

P0134, P0135, P0154, P0155

--

--

Typical Scan Tool Data

Bank 1 or 2 HO2S  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

400-455 mV

1275 mV

Low Reference

--

400-455 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 DTCs

P0137 and P0157

    • DTCs P0117, P0118, P0125, and P0128 are not set.
    • The HO2S heater is at operating temperature.
    •  The engine is operating for greater than 1 second.
    • The ignition voltage is more than 10.5 volts.
    • The engine coolant temperature is less than 40°C (104°F) at start-up and the engine coolant temperature was more than 60°C (140°F) when the ignition was turned OFF last ignition cycle.
    •  The calculated exhaust temperature is between 250-800°C (482-1,472°F) for more than 90 seconds.
    • DTCs P0137 and P0157 run continuously once the above conditions are met.

P0138, P0140, P0158, and P0160

    • The HO2S heater is at operating temperature.
    •  The engine is operating for greater than 1 second.
    • The ignition voltage is more than 10.5 volts.
    •  The calculated exhaust temperature is between 250-800°C (482-1,472°F) for more than 90 seconds.
    • DTCs P0138 and P0158 run continuously once the above conditions are met for greater than 5 seconds.
    • DTCs P0140 and P0160 run continuously once the above conditions are met for greater than 60 seconds.

Conditions for Setting the DTC

P0137 or P0157

The ECM detects that a secondary HO2S signal voltage is less than 60 mV for greater than 4 seconds of for a cumulative of 50 seconds.

P0138 or P0158

The ECM detects that the HO2S signal voltage is more than 1,080 mV for greater than 4 seconds or for a cumulative of 50 seconds.

P0140 or P0160

    • The ECM detects that the HO2S voltage is between 401-519 mV .
    •  The ECM detects that the measured internal resistance of the HO2S is greater than 40,000 ohms, when the calculated exhaust temperature is greater than 600°C (1,112°F).
    • Either condition exists for greater than 4 seconds or for a cumulative of 50 seconds.

Action Taken when the DTC Sets

DTCs P0137, P0138, P0140, P0157, P0158, and P0160 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0137, P0138, P0140, P0157, P0158, and P0160 are Type B DTCs.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls 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

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls

Circuit/System Verification

  1. With the engine running, observe the heated oxygen sensor (HO2S) voltage parameter. The reading should fluctuate above and below the range of 350-550 mV.
  2. If the vehicle passes the Circuit/System Verification Test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

Circuit/System Testing

  1. Ignition OFF, disconnect the harness connector at the appropriate HO2S.
  2. Ignition ON, verify that the applicable HO2S voltage parameter is between 350-500 mV.
  3. If less than the specified value, test the signal circuit for a short to ground. If the circuit/connections test normal, replace the ECM.
    If greater than the specified value, test the signal circuit for a short to voltage. If the circuit/connections test normal, replace the ECM.
  4. Install a 3A 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 value, test the signal circuit for an open/high resistance. If the circuit/connections test normal, replace the ECM.
  6. Connect a 3A 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 value, 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, rich, or leaking fuel injectors--Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2 .
    • A fuel pressure that is too low or too high--Refer to Fuel System Diagnosis .
    • Fuel that is contaminated--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Evidence of water intrusion into the electrical connector of the HO2S
    • The HO2S is loose
    • 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 HO2S sensor.

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 2
    •  Control Module References for engine control module replacement, setup, and programming