DTC B278A: Short to GND in Immobiliser System Power Source Circuit [08/2019 - ]: Procedure

1. Using an oscilloscope, check the waveform.

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   *a

   Component with harness connected (Engine Switch)

   *b

   Waveform

   OK

   Tester Connection	Condition	Tool Setting	Specified Condition
   H201-10 (VC5) - H201-6 (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 [08/2019 - ] 

Result: 

NG 

See step  2

1. Disconnect the H199 certification ECU (smart key ECU assembly) connector.
2. Disconnect the H201 engine switch connector.
3. Measure the resistance according to the value(s) in the table below.

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   H199-15 (VC5) - H201-10 (VC5)	Always	Below 1 Ω
   H199-15 (VC5) or H201-10 (VC5) - Other terminals and body ground	Always	10 kΩ or higher
   H199-12 (AGND) - H201-6 (AGND)	Always	Below 1 Ω

4. Reconnect the H199 certification ECU (smart key ECU assembly) connector.
5. Reconnect the H201 engine switch connector.

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPAIR OR REPLACE HARNESS OR CONNECTOR 

Result: 

OK 

See step  3

1. 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
   H199-15 (VC5) - H199-12 (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 [08/2019 - ] 

Result: 

NG 

REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY). Refer to  REMOVAL [08/2019 - ]