DTC B278A: Short to GND in Immobiliser System Power Source Circuit [10/2018 - 07/2022]: Procedure

1. Using an oscilloscope, check the waveform.

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   *a

   Component with harness connected (Engine Switch)

   *b

   Waveform

   HINT: 

   Perform this inspection on the engine switch side.

   OK

   Tester Connection	Condition	Tool Setting	Specified Condition
   F47-10 (VC5) - F47-6 (AGND)	Engine switch off, electrical key transmitter sub-assembly not in cabin, within 30 seconds of 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 [10/2018 - 07/2022] 

Result: 

NG 

See step  2

1. Disconnect the F44 certification ECU (smart key ECU assembly) connector.
2. Disconnect the F47 engine switch connector.
3. Measure the resistance according to the value(s) in the table below.

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   F44-7 (VC5) - F47-10 (VC5)	Always	Below 1 Ω
   F44-11 (AGND) - F47-6 (AGND)	Always	Below 1 Ω
   F44-7 (VC5) or F47-10 (VC5) - Other terminals and body ground	Always	10 kΩ or higher
   F44-11 (AGND) or F47-6 (AGND) - Other terminals and body ground	Always	10 kΩ or higher

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPAIR OR REPLACE HARNESS OR CONNECTOR 

Result: 

OK 

See step  3

1. Connect the F44 certification ECU (smart key ECU assembly) connector.
2. Connect the F47 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
   F44-7 (VC5) - F44-11 (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 [10/2018 - 07/2022] 

Result: 

NG 

REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY). Refer to  REMOVAL [10/2018 - 07/2022]