ENGINE IMMOBILISER SYSTEM (w/ Smart Entry and Start System), Diagnostic DTC:B278A

DTC Code DTC Name
B278A Short to GND in Immobiliser System Power Source Circuit

DESCRIPTION

This DTC is output when the engine switch power source supply line is open or shorted.

DTC No. DTC Detection Condition Trouble Area
B278A Engine switch power source supply line is open or shorted

  • Wire harness or connector

  • Engine switch

  • Certification ECU (Smart key ECU assembly)

WIRING DIAGRAM

A017BPEE04

INSPECTION PROCEDURE

Note

If the certification ECU (smart key ECU assembly) is replaced, register the key and ECU communication ID.

PROCEDURE


  1. CHECK DTC OUTPUT


    1. Delete the DTCs Click here.

    2. Recheck for DTCs.

      OK
      B278A output does not recur.

    NG

    CHECK HARNESS AND CONNECTOR (CERTIFICATION ECU - ENGINE SWITCH) Click here

    OK

    USE SIMULATION METHOD TO CHECK Click here

  2. CHECK HARNESS AND CONNECTOR (CERTIFICATION ECU - ENGINE SWITCH)


    1. A017FIVE02

      Disconnect the certification ECU (smart key ECU assembly) and engine switch connectors.

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

      Standard resistance
      Tester Connection Condition Specified Condition
      D36-30 (VC5) - D22-14 (VC5) Always Below 1 Ω
      D36-40 (AGND) - D22-8 (AGND) Always Below 1 Ω
      D36-17 (E) - Body ground Always Below 1 Ω
      D36-30 (VC5) - Body ground Always 10 kΩ or higher
      D36-40 (AGND) - Body ground Always 10 kΩ or higher

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

  3. CHECK HARNESS AND CONNECTOR (ENGINE SWITCH POWER SOURCE)


    1. A017FMZE01

      Reconnect the certification ECU (smart key ECU assembly) and engine switch connectors.

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

      Standard voltage
      Tester Connection Condition Specified Condition
      D36-30 (VC5) - Body ground Engine switch off, brake pedal not depressed, 30 seconds or more elapsed after driver door opened and then closed Below 1 V
    3. A017BJ4E01

      Using an oscilloscope, check the waveform.

      Measurement condition
      Tester Connection Condition Tool Setting Specified Condition
      D36-30 (VC5) - Body ground Engine switch off, key not in cabin, within 30 seconds after engine switch pressed 2 V/DIV., 200 ms./DIV. Pulse generation
      OK
      The waveform is similar to that shown in the illustration.

    NG

    REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY)

    OK

  4. CHECK HARNESS AND CONNECTOR (ENGINE SWITCH BODY GROUND)


    1. A017FMZE02

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

      Standard resistance
      Tester Connection Condition Specified Condition
      D36-40 (AGND) - Body ground Always Below 1 Ω

    NG

    REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY)

    OK

    REPLACE ENGINE SWITCH Click here