Toyota 4Runner Quiz
Vehicle Interior

Short to GND in Immobiliser System Power Source Circuit (B278A)

In this manual: Vehicle Interior
General — 25Audio / Visual / Telematics — 283Brake — 187Drivetrain — 204Power Source / Network — 79Steering — 76Suspension — 130Vehicle Exterior — 391Vehicle Interior — 693
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DESCRIPTION

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

DTC Code

DTC Detection Condition

Trouble Area

B278A

The engine switch power source supply line is open or shorted.
  • Harness or connector
  • Engine switch
  • Certification ECU
WIRING DIAGRAM
CAUTION / NOTICE / HINT

NOTICE:

Before replacing the certification ECU, refer to Registration (See page ).


PROCEDURE

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

(a) Disconnect the F79 ECU connector.

(b) Disconnect the F71 switch connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

F79-28 (VC5) - F71-14 (VC5)

Always

Below 1 Ω

F79-36 (AGND) - F71-8 (AGND)

F79-28 (VC5) or F71-14 (VC5) - Body ground

Always

10 kΩ or higher

F79-36 (AGND) or F71-8 (AGND) - Body ground

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

  1. CHECK CERTIFICATION ECU

(a) Using an oscilloscope, check the waveform.

Measurement Condition

Item

Content

Tester Connection

F71-14 (VC5) - F71-8 (AGND)

Tool Setting

2 V/DIV., 20 ms./DIV.

Condition

Engine switch off, key not in cabin and 30 seconds or less after engine switch pushed

OK:

Waveform is output normally (refer to illustration).

Text in Illustration

*a

Component with harness connected

(Engine Switch)

OK

REPLACE ENGINE SWITCH

NG

REPLACE CERTIFICATION ECU

Test yourself

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