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DTC B278A: Short to GND in Immobilizer System Power Source Circuit [10/2022 - 11/2023]: Procedure

  1. CHECK CERTIFICATION ECU (SMART KEY ECU ASSEMBLY) 
    1. Using an oscilloscope, check the waveform.
      GTY930087Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Component with harness connected
      (Engine Switch)      		 - -

      HINT: 

      Perform this inspection on the engine switch side.

      Measurement Condition

      Tester Connection Condition Tool Setting Specified Condition
      H49-10 (VC5) - H49-6 (AGND) Ignition switch off, electrical key transmitter sub-assembly not in cabin, within 30 seconds of engine switch pressed 2 V/DIV., 200 ms./DIV. Pulse generation

      OK

      The waveform is similar to that shown in the illustration.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE ENGINE SWITCH. Refer to  REMOVAL [10/2022 - 11/2023] 

    Result: 

    NG 

    See step  2

  2. CHECK HARNESS AND CONNECTOR (CERTIFICATION ECU (SMART KEY ECU ASSEMBLY) - ENGINE SWITCH) 
    1. Disconnect the H48 certification ECU (smart key ECU assembly) connector.
    2. Disconnect the H49 engine switch connector.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      H48-7 (VC5) - H49-10 (VC5) Always Below 1 Ω
      H48-11 (AGND) - H49-6 (AGND) Always Below 1 Ω
      H48-7 (VC5) or H49-10 (VC5) - Other terminals and body ground Always 10 kΩ or higher
      H48-11 (AGND) or H49-6 (AGND) - Other terminals and body ground Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  3

  3. CHECK CERTIFICATION ECU (SMART KEY ECU ASSEMBLY) 
    1. Connect the H48 certification ECU (smart key ECU assembly) connector.
    2. Connect the H49 engine switch connector.
    3. Measure the voltage according to the value(s) in the table below.
      GTY930651Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Component with harness connected
      (Certification ECU (Smart Key ECU Assembly))      		 - -

      Standard Voltage

      Tester Connection Condition Specified Condition
      H48-7 (VC5) - H48-11 (AGND) Ignition switch off, brake pedal not depressed, 30 seconds or more after driver door opened and then closed Below 1 V

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE ENGINE SWITCH. Refer to  REMOVAL [10/2022 - 11/2023] 

    Result: 

    NG 

    REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY). Refer to  REMOVAL [12/2019 - 11/2023] 

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