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DTC P1138 (LLU)

DTC P1138 (LLU)

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 Descriptor

DTC P1138 00

HO2S Circuit High Voltage During Deceleration Fuel Cut-Off Sensor 2

Typical Scan Tool Data

HO2S Sensor 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

Signal HO2S Sensor 2

0 V

400-415 mV

1000 mV

Low Reference

-

400-415 mV

1000 mV



Circuit/System 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 0-1000 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 1000 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 sensors utilizes the following circuits:


• A signal circuit

• A low reference

• An ignition voltage circuit

• A heater control circuit


Conditions for Running the DTC


• DTCs P0036 00, P0101 00, P0102 00, P0103 00, P0121 00, P0122 00, P0123 00, P0137 00, P0138 00, P0140 00, P0141 00, P0171 00, P0172 00, P0221 00, P0222 00, P0223 00, P0300 00, P0301 00, P0302 00, P0303 00, P0304 00, P0458 00, and P0459 00 are not set.

• The engine is in deceleration fuel cut off mode.

• The mass airflow is between 15-90 g/s.

• The ignition voltage is between 10-16 volts.

• The DTCs run continuously when the above conditions are met for 1 second.


Conditions for Setting the DTC

The engine control module (ECM) detects that the HO2S Sensor 2 voltage is greater than 550 mV during deceleration fuel cut off mode.

Action Taken When the DTC Sets

DTC P1138 00 is a Type B DTC.

Conditions for Clearing the DTC

DTC P113 008 is a Type B DTC.

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 running, observe the scan tool HO2S sensor 2 voltage parameter. The reading 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 B52B Heated Oxygen Sensor 2.

2. Ignition OFF, test for less than 5 Ω of resistance between the low reference circuit terminal 3 and ground.

3. If greater than the specified range, test the low reference circuit for a short to voltage, or an open/high resistance. If the circuit tests normal, replace the K20 Engine Control Module.

4. Engine running, verify the scan tool HO2S Sensor 2 parameter is between 350-500 mV

5. If greater than the specified value, test signal circuit terminal 4 for the B52B heated oxygen sensor 2 for a short to voltage. If the circuit tests normal, replace the K20 engine control module.

6. Verify none of the following conditions exist:

• Rich fuel injectors-Refer to Fuel Injector Diagnosis

• Water intrusion in the B52B Heated Oxygen Sensor 2 harness connector

• High fuel system pressure-Refer to Fuel System Diagnosis .

• Fuel that is contaminated-Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• Fuel saturation of the evaporative emission (EVAP) canister

• Exhaust leaks near the B52B Heated Oxygen Sensor 2

• Silicon contaminated B52B Heated Oxygen Sensor 2

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

7. If all circuits test normal, replace the B52B Heated Oxygen Sensor 2.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Heated Oxygen Sensor Replacement - Sensor 2

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