SFI SYSTEM, Diagnostic DTC:P0138

DTC Code DTC Name
P0138 Oxygen Sensor Circuit High Voltage (Bank 1 Sensor 2)

DESCRIPTION

In order to obtain a high purification rate for the carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) components in the exhaust gas, a Three-Way Catalytic Converter (TWC) is used. For the most efficient use of the TWC, the air fuel ratio must be precisely controlled so that it is always close to the stoichiometric air fuel ratio. The No. 2 heated oxygen sensor has the characteristic whereby its output voltage changes suddenly in the vicinity of the stoichiometric air fuel ratio. This is used to detect the oxygen concentration in the exhaust gas and provide the ECM with feedback to control the air fuel ratio. When the air fuel ratio becomes lean, the oxygen concentration in the exhaust gas increases. The No. 2 heated oxygen sensor informs the ECM of the lean condition (low voltage, i.e. less than 0.45 V). When the air fuel ratio is richer than the stoichiometric air fuel level, the oxygen concentration in the exhaust gas is reduced, and the No. 2 heated oxygen sensor informs the ECM of the rich condition (high voltage, i.e. more than 0.45 V). The ECM judges, using the voltage output of the No. 2 heated oxygen sensor, whether the air fuel ratio is rich or lean and controls the injection time accordingly. If a malfunction of the No. 2 heated oxygen sensor causes an output of abnormal voltage, the ECM is unable to perform accurate air fuel ratio control. The No. 2 heated oxygen sensor includes a heater which heats the zirconia element. The heater is controlled by the ECM. When the intake air volume is low (the temperature of the exhaust gas is low), a current flows to the heater in order to heat the sensor for accurate oxygen concentration detection.

A01VGWJE10
DTC No. DTC Detection Condition Trouble Area
P0138 No. 2 heated oxygen sensor output voltage is 1.5 V or more continuously for 5.1 seconds (3 trip detection logic)

  • Short in signal output circuit and power source circuit of No. 2 heated oxygen sensor

  • No. 2 heated oxygen sensor

  • ECM

Tech Tips

The normal output voltage from the No. 2 heated oxygen sensor is 0 to 1.0 V.

WIRING DIAGRAM

Refer to DTC P0130 Click here.

CONFIRMATION DRIVING PATTERN

CAUTION:

When performing the confirmation driving pattern, obey all speed limits and traffic laws.

DTC P0138 is detected when the vehicle is driven with a city driving pattern at an average vehicle speed of approximately 50 km/h (30 mph) for approximately 30 minutes.

CAUTION / NOTICE / HINT

Note


  • Perform electronic throttle learning after replacing the ECM Click here.

  • Inspect the fuses for circuits related to this system before performing the following inspection procedure.

Tech Tips


  • Inspect the No. 2 heated oxygen sensor output voltage:

    Read the No. 2 heated oxygen sensor output voltage using the intelligent tester


    1. Connect the intelligent tester to the DLC3.

    2. Start the engine.

    3. Turn the tester on.

    4. Enter the following menus: Powertrain / Engine and ECT / Data List / O2S B1S2.

    5. Read the output voltage of the No. 2 heated oxygen sensor.

      Standard voltage
      No. 2 Heated Oxygen sensor 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 intelligent tester. 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. INSPECT NO. 2 HEATED OXYGEN SENSOR

    A01VK69E02
    Text in Illustration
    *a

    Component without harness connected

    (No. 2 Heated Oxygen Sensor)

    1. Disconnect the No. 2 heated oxygen sensor connector.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      2 (+B) - 3 (OX1B) Always 10 kΩ or higher

    NG

    REPLACE NO. 2 HEATED OXYGEN SENSOR Click here

    OK

  2. CHECK HARNESS AND CONNECTOR (NO. 2 HEATED OXYGEN SENSOR - ECM)


    1. Disconnect the No. 2 heated oxygen sensor connector.

    2. Disconnect the ECM connector.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      B87-36 (OX1B) - B87-41 (HT1B) Always 10 kΩ or higher

    OK

    REPLACE ECM Click here

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR