Toyota Tacoma (2015-2018) Service Manual: Short to GND in Immobiliser System Power Source Circuit (B278A)

Toyota Tacoma (2015-2018) Service Manual / Engine Immobiliser / Engine Immobiliser System(w/ Smart Key System) / Short to GND in Immobiliser System Power Source Circuit (B278A)

DESCRIPTION

When there is a short to GND in the power supply for the transponder key amplifier of the engine 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 engine switch (VC5 - VC5) (1 trip detection logic*).	Wire harness or connector Engine switch Certification ECU (smart key ECU assembly)	With the shift lever in P, the key held near the engine switch and an engine start operation is performed by pressing and holding the engine switch when the key battery is depleted.

*: 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
Engine cannot be started when key battery is depleted by holding key near engine switch and pressing and holding engine switch with shift lever in P	-

Related Data List and Active Test

DTC Code	Data List and Active Test
B278A	-

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

Before replacing the certification ECU (smart key ECU assembly), refer to Registration (See page ).
After performing repairs, perform the operation that fulfills the DTC output confirmation operation, and then confirm that no DTCs are output again.

PROCEDURE

1.	CHECK CERTIFICATION ECU (SMART KEY ECU ASSEMBLY)

(a) Using an oscilloscope, check the waveform.

Text in Illustration

Component with harness connected

(Engine Switch)

Waveform

HINT:

Perform this inspection on the engine switch side.

Measurement Condition:

Tester Connection	Condition	Tool Setting	Specified Condition
E28-10 (VC5) - E28-6 (AGND)	Engine switch off, key not in cabin, within 30 seconds after engine switch pressed	2 V/DIV., 200 ms./DIV.	Pulse generation (See waveform)

Tester Connection

Condition

Tool Setting

Specified Condition

E28-10 (VC5) - E28-6 (AGND)

Engine switch off, key not in cabin, within 30 seconds after engine switch pressed

2 V/DIV., 200 ms./DIV.

Pulse generation

(See waveform)

OK:

The waveform is similar to that shown in the illustration.

Result

Result	Proceed to
NG	A
OK	B

REPLACE ENGINE SWITCH

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

(a) Disconnect the C29 certification ECU (smart key ECU assembly) connector.

(b) Disconnect the E28 engine switch connector.

Standard Resistance:

Tester Connection	Condition	Specified Condition
C29-15 (VC5) - E28-10 (VC5)	Always	Below 1 Ω
C29-12 (AGND) - E28-6 (AGND)	Always	Below 1 Ω
C29-15 (VC5) or E28-10 (VC5) - Body ground	Always	10 kΩ or higher
C29-12 (AGND) or E28-6 (AGND) - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

3.	CHECK CERTIFICATION ECU (SMART KEY ECU ASSEMBLY)

(a) Reconnect the C29 certification ECU (smart key ECU assembly) connector.

(b) Reconnect the E28 engine switch connector.

Text in Illustration

Component with harness connected

(Certification ECU (Smart Key ECU Assembly))

Standard Voltage:

Tester Connection	Condition	Specified Condition
C29-15 (VC5) - C29-12 (AGND)	Engine switch off, brake pedal not depressed, 30 seconds or more elapsed after driver door opened and then closed	Below 1 V

REPLACE ENGINE SWITCH

REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY)

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Other materials:

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Data List / Active Test
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