Toyota 4Runner: Short to GND in Immobiliser System Power Source Circuit (B278A)

Toyota 4Runner Service Manual / Vehicle Interior / Theft Deterrent / Keyless Entry / Engine Immobiliser System(w/ Smart Key System) / Short to GND in Immobiliser System Power Source Circuit (B278A)

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.

Standard Resistance:

Tester Connection	Condition	Specified Condition
F79-28 (VC5) - F71-14 (VC5)	Always	Below 1 Ω
F79-36 (AGND) - F71-8 (AGND)	Always	Below 1 Ω
F79-28 (VC5) or F71-14 (VC5) - Body ground	Always	10 kΩ or higher
F79-36 (AGND) or F71-8 (AGND) - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

2.	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)

REPLACE ENGINE SWITCH

REPLACE CERTIFICATION ECU

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