Toyota Tacoma manuals

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

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 ).
  • 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

*a

Component with harness connected

(Engine Switch)

*b

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)

OK:

The waveform is similar to that shown in the illustration.

Result

Result

Proceed to

NG

A

OK

B

B

REPLACE ENGINE SWITCH

A

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.

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

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

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

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.

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

Text in Illustration

*a

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

OK

REPLACE ENGINE SWITCH

NG

REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY)

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