DTC B278A: Short to GND in Immobiliser System Power Source Circuit [12/2017 - 10/2023]: Procedure

1. Using an oscilloscope, check the waveform.

   HINT: 

   Perform this inspection on the push engine switch side.

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   OK

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

   Result

   Proceed to
   OK
   NG

Result: 

OK 

REPLACE ENGINE SWITCH. Refer to  REMOVAL [12/2017 - 10/2020]  , or refer to  REMOVAL [10/2020 - ] 

Result: 

NG 

See step  2

1. Disconnect the G71 certification ECU (smart key ECU assembly) connector.
2. Disconnect the A engine switch connector.
3. Measure the resistance according to the value(s) in the table below.

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   G71-7 (VC5) - A-10 (VC5)	Always	Below 1 Ω
   G71-7 (VC5) or A-10 (VC5) - Other terminals and body ground	Always	10 kΩ or higher
   G71-11 (AGND) - A-6 (AGND)	Always	Below 1 Ω

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPAIR OR REPLACE HARNESS OR CONNECTOR 

Result: 

OK 

See step  3

1. Reconnect the G71 certification ECU (smart key ECU assembly) connector.
2. Reconnect the A engine switch connector.
3. Measure the voltage according to the value(s) in the table below.

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   *a

   Component with harness connected (Certification ECU (Smart Key ECU Assembly))

   -

   -

   Standard Voltage

   Tester Connection	Condition	Specified Condition
   G71-7 (VC5) - G71-11 (AGND)	Engine switch off, brake pedal not depressed, 30 seconds or more after driver door opened and then closed	Below 1 V

   Result

   Proceed to
   OK
   NG

Result: 

OK 

REPLACE ENGINE SWITCH. Refer to  REMOVAL [12/2017 - 10/2020]  , or refer to  REMOVAL [10/2020 - ] 

Result: 

NG 

REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY). Refer to  REMOVAL [12/2017 - 09/2018]  , or refer to  REMOVAL [09/2018 - 10/2020]  , or refer to  REMOVAL [10/2020 - 10/2022]  , or refer to  REMOVAL [10/2022 - 10/2023]