DTC    B278A    Short to GND in Immobiliser System Power Source Circuit

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DESCRIPTION

When there is a short to GND in the power supply for the transponder key amplifier of the power switch, the certification ECU (smart key ECU assembly) stores this DTC.

DTC Code
DTC Detection Condition
Trouble Area
DTC Output Confirmation Operation
B278A
A short to GND in the power supply of the transponder key amplifier of the power switch (VC5 - VC5) (1 trip detection logic*).
  1. Wire harness or connector
  1. Power switch
  1. Certification ECU (smart key ECU assembly)
With park (P) selected, the key is held against the power switch and a hybrid control system start operation is performed by pressing and holding the power switch when the key battery is depleted.
  1. *: Only output while a malfunction is present.

Vehicle Condition and Fail-safe Operation when Malfunction Detected 
Vehicle Condition when Malfunction Detected
Fail-safe Operation when Malfunction Detected
Hybrid control system cannot be started when key battery is depleted by holding key against power switch and pressing and holding power switch with park (P) selected
-

Related Data List and Active Test 
DTC Code
Data List and Active Test
B278A
-

WIRING DIAGRAM


B153714E45


INSPECTION PROCEDURE

NOTICE:
  1. Before replacing the certification ECU (smart key ECU assembly), refer to the Service Bulletin.
  2. The fixed 5 V power source voltage in the power switch is output through a resistance from terminal VC5.
  3. Terminal AGND is grounded through both the power switch and certification ECU (smart key ECU assembly).
  4. After performing repair, perform the operation that fulfills the DTC output confirmation operation, and then confirm that no DTCs are output again.

1.CHECK HARNESS AND CONNECTOR (CERTIFICATION ECU - POWER SWITCH)

  1. Disconnect the H1*1 or H143*2 ECU connector.

    1. *1: w/ Entry Function
    2. *2: w/o Entry Function

  1. Disconnect the H78 switch connector.

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

    Standard Resistance:
    Tester Connection
    		Condition
    		Specified Condition
    H1-28 (VC5) - H78-14 (VC5)*1
    H143-28 (VC5) - H78-14 (VC5)*2
    		Always
    		Below 1 Ω
    H1-36 (AGND) - H78-8 (AGND)*1
    H143-36 (AGND) - H78-8 (AGND)*2
    H1-28 (VC5) or H78-14 (VC5) - Body ground*1
    H143-28 (VC5) or H78-14 (VC5) - Body ground*2
    		Always
    		10 kΩ or higher
    H1-36 (AGND) or H78-8 (AGND) - Body ground*1
    H143-36 (AGND) or H78-8 (AGND) - Body ground*2

    1. *1: w/ Entry Function
    2. *2: w/o Entry Function



NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
OK


2.CHECK CERTIFICATION ECU (SMART KEY ECU ASSEMBLY)


    B226518E13

  1. Using an oscilloscope, check the waveform.

    HINT:
    Perform this inspection on the power switch side.

    Measurement Condition 
    Item
    		Content
    Tester Connection
    		H78-14 (VC5) - H78-8 (AGND)
    Tool Setting
    		2 V/DIV., 200 ms./DIV.
    Condition
    		After power switch turned off, within 30 seconds of any door opened and closed, or brake pedal depressed

    OK:
    Waveform is output normally (refer to illustration).

    Text in Illustration 
    *a
    		Component with harness connected
    (Power Switch)



NG
REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY)
OK

REPLACE POWER SWITCH (Click here)