SFI SYSTEM, Diagnostic DTC:P0138

DTC Code DTC Name
P0138 O2 Sensor Circuit High Voltage Bank 1 Sensor 2

DESCRIPTION

DTC No. Detection Item DTC Detection Condition Trouble Area MIL Memory
P0138 O2 Sensor Circuit High Voltage Bank 1 Sensor 2

DTC Detection Condition


    Enable Criteria

  • Engine running


    Malfunction Criteria

  • Set when the sensor operates above 1.20 V for more than 7.5 seconds consecutively for a specified number of times


    Diagnostic Mask

  • The MIL will be illuminated if these faults are present for 2 consecutive trips


    Monitor

  • Continuous


    Potential failure modes

  • Check and rectify any front sensor fault code, as they may be causing the fault code to be set

  • Catalyst

  • Short in signal output circuit and power source circuit of heated oxygen sensor (sensor 2)

  • Heated oxygen sensor (sensor 2)

  • ECM

 Comes on DTC stored

MONITOR DESCRIPTION

The oxygen sensor is electrically heated to improve response from start.

The sensor consists of zirconia electrode between two platinum plates. When zirconia comes into contact with oxygen, it becomes an electrical conductor. The exhaust gases passes through louvers in the sensor. One plate is in contact with the outside air and the other plate is in contact with the exhaust gases. The platinum plate in contact with the air is electrically negative due to the oxygen in the atmosphere and the plate in contact with the exhaust gases is electrically positive. This will cause a difference in electrical potential to develop between the two plates. Thus the voltage across the platinum plates ranges approximately from 100 millivolts to 900 millivolts, depending on the oxygen content of the exhaust gases. Thus when the air/fuel mixture is rich, the oxygen sensor output will be high. If the air/fuel mixture is lean, the oxygen sensor output will be low. The post catalyst oxygen sensor performance is a good indicator of catalyst efficiency.

"O2 Sensor, slow response" can be defined in two ways; 1) "Slow response" and 2) Delayed response

1) Slow ResponseSet when the sensor fails to reach 600mV after 5 seconds of Fuel Enrichment or when the sensor fails to drop below 322mV after 5 seconds of DFCO.

2) Delayed ResponseSet when the sensor fails to switch between 300mV and 600mV within a specified time of the pre cat O2 sensor switch.

WIRING DIAGRAM

Refer to DTC P0131.

Click here

CAUTION / NOTICE / HINT

Tech Tips


  • Inspect the heated oxygen sensor (sensor 2) output voltage:

    Read the heated oxygen sensor (sensor 2) output voltage using the GTS.


    1. Connect the GTS to the DLC3.

    2. Start the engine.

    3. Turn the GTS on.

    4. Allow the engine to idle for 20 minutes or more.

    5. Enter the following menus: Powertrain / Engine / Data List / All Data / O2S B1S2.

    6. Read the output voltage of the heated oxygen sensor (sensor 2).

      Standard voltage
      Heated oxygen sensor (sensor 2) output is below 1.0 V.

  • Sensor 1 refers to the sensor closest to the engine assembly.

  • Sensor 2 refers to the sensor farthest away from the engine assembly.

  • Read freeze frame data using the GTS. Freeze frame data records the engine condition when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, if the air fuel ratio was lean or rich, and other data from the time the malfunction occurred.

PROCEDURE


  1. CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0138)


    1. Connect the GTS to the DLC3.

    2. Turn the engine switch on (IG).

    3. Turn the GTS on.

    4. Enter the following menus: Powertrain / Engine / Trouble Codes.

    5. Read the DTCs.

      Result
      Result Proceed to
      DTC P0138 is output A
      DTC P0138 and other DTCs are output B

      Tech Tips

      If any DTCs other than P0138 are output, troubleshoot those DTCs first.


    B

    GO TO DTC CHART Click here

    A

  2. INSPECT HEATED OXYGEN SENSOR (SENSOR 2)

    B004869C18
    *a

    Component without harness connected

    (Heated Oxygen Sensor (Sensor 2))

    1. Disconnect the F142 heated oxygen sensor (sensor 2) connector.

    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance
      Tester Connection Condition Specified Condition
      2 (DIL+) - 3 (OX1B) Always 10 kΩ or higher
      2 (DIL+) - 4 (E2) Always 10 kΩ or higher
      Result
      Proceed to
      OK
      NG

    NG

    REPLACE HEATED OXYGEN SENSOR (SENSOR 2) Click here

    OK

  3. CHECK HARNESS AND CONNECTOR (HEATED OXYGEN SENSOR (SENSOR 2) - ECM)


    1. Disconnect the F142 heated oxygen sensor (sensor 2) connector.

    2. Disconnect the B142 ECM connector.

    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance
      Tester Connection Condition Specified Condition
      F142-3 (OX1B) - F142-1 (HT1B) Always 10 kΩ or higher
      Result
      Proceed to
      OK
      NG

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

  4. CHECK WHETHER DTC OUTPUT RECURS (DTC P0138)


    1. Connect the GTS to the DLC3.

    2. Turn the engine switch on (IG).

    3. Turn the GTS on.

    4. Clear the DTCs.

    5. Turn the engine switch off and wait for at least 30 seconds.

    6. Start the engine and warm it up.

    7. Turn the GTS on.

    8. Enter the following menus: Powertrain / Engine / Trouble Codes.

    9. Read the DTCs.

      Result
      Result Proceed to
      DTC P0138 is output A
      DTCs are not output B

    A

    REPLACE ECM Click here

    B

    CHECK FOR INTERMITTENT PROBLEMS Click here