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Home >> Chevrolet >> 2006 >> Optra (CANADA) L4-2.0L >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> P Code Charts >> P0138

P0138




DTC P0131, P0132, P0134, P0137, P0138, or P0140

DTC Descriptors
DTC P0131
- HO2S Circuit Low Voltage Sensor 1

DTC P0132
- HO2S Circuit High Voltage Sensor 1

DTC P0134
- HO2S Circuit Insufficient Activity Sensor 1

DTC P0137
- HO2S Circuit Low Voltage Sensor 2

DTC P0138
- HO2S Circuit High Voltage Sensor 2

DTC P0140
- HO2S Circuit Insufficient Activity Sensor 2

Diagnostic Fault Information

Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.






Typical Scan Tool Data






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.

The HO2S utilizes the following circuits:

* A signal circuit
* A low reference circuit
* An ignition 1 voltage circuit
* A heater control circuit

Conditions for Running the DTC

* The calculated airflow into the engine is greater than 6 g/s.
* The startup engine coolant temperature is greater than 60°C (140°F).
* The ignition 1 voltage is greater than 10 volts.
* The fuel system is in Closed Loop.
* The engine has been operating for 10 seconds.
* The vehicle is not decelerating.
* The DTCs run continuously when the above conditions are met for 3 seconds.

Conditions for Setting the DTC

P0131 or P0137

The engine control module (ECM) detects that the HO2S 1 voltage is less than 50 mV.

P0132 or P0138

The ECM detects that the HO2S 1 voltage is greater than 950 mV.

P0134 or P0140

The ECM detects that the HO2S 1 voltage is between 299-303 mV.

Action Taken when the DTC Sets

DTCs P0131, P0132, P0134, P0137, P0138, and P0140 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0131, P0132, P0134, P0137, P0138, and P0140 are Type B DTCs.

Reference Information

Schematic Reference

Engine Controls Schematics Electrical Diagrams

Connector End View Reference
* Engine Control Module (ECM) Connector End Views Engine Control Module (ECM) Connector End Views
* Engine Controls Connector End Views Engine Controls Connector End Views

Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs

DTC Type Reference

Diagnostic Trouble Code (DTC) Type Definitions Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference
* Scan Tool Data List Scan Tool Data List
* Scan Tool Data Definitions Scan Tool Data Definitions
* Scan Tool Output Controls Scan Tool Output Controls

Circuit/System Verification

1. With the engine running, observe the applicable heated oxygen sensor 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 of the applicable HO2S.
2. Ignition ON, verify that the applicable HO2S parameter is between 350-500 mV.

• If less than 350 mV, test the signal circuit of the HO2S for a short to ground. If the circuit/connections test normal, replace the ECM.

• If greater than 500 mV, test the signal circuit of the HO2S for a short to voltage. If the circuit/connections test normal, replace the ECM.

Important: The test lamp is used to load the circuit and may not illuminate.


3. Connect a test lamp between the low reference circuit of the HO2S and B+.
4. Ignition ON, test for less than 0.1 volt between the low reference circuit of the HO2S and ground.

• If greater than 0.1 volt, test the low reference circuit of the HO2S for a short to voltage or an open/high resistance. If the circuit/connections test normal, replace the ECM.

5. Install a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the HO2S and verify the HO2S parameter is less than 60 mV.

• If greater than 60 mV, test the signal circuit of the HO2S for an open/high resistance. If the circuit/connections test normal, replace the ECM.

6. Verify that none of the following conditions exist:

* Lean or rich fuel injectors-Refer to Fuel Injector Balance Test with Special Tool Fuel Injector Balance Test with Special Tool.
* Water intrusion in the HO2S harness connector
* Low or high fuel system pressure-Refer to Fuel System Diagnosis Fuel System Diagnosis.
* Fuel that is contaminated-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool)Alcohol/Contaminants-in-Fuel Diagnosis (w/Special tool) Alcohol/Contaminants-in-Fuel Diagnosis (w/Special tool).
* Fuel saturation of the evaporative emission (EVAP) canister
* Exhaust leaks near the HO2S
* Engine vacuum leaks

• If you find any of the above conditions, repair as necessary.

7. If all circuits/connections test normal, replace the applicable HO2S.

Repair Instructions

Important: Always perform the Diagnostic Repair Verification Diagnostic Repair Verification after completing the diagnostic procedure.


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

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