DTC B278C: Lost Communication with Power Source Control: Procedure

1. Disconnect the L5 and L6 power management control ECU connectors.
   Fig 1: Identifying Harness And Connector (Power Management Control ECU - Battery And Body Ground)

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Measure the resistance and voltage according to the value(s) in the table below.

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   L5-6 (E1) - Body ground	Always	Below 1 Ω

   Standard Voltage

   Tester Connection	Condition	Specified Condition
   L5-1 (AM22) - Body ground	Power switch off	11 to 14 V
   L6-7 (AM21) - Body ground	Power switch off	11 to 14 V

   TEXT IN ILLUSTRATION
   
   

   *1	Front view of wire harness connector (to Power Management Control ECU)

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK: Go to next step 

1. Disconnect the L62 certification ECU (smart key ECU assembly) connector.
   Fig 2: Identifying Certification ECU And Power Management Control ECU Connector Terminals

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Measure the resistance according to the value(s) in the table below.

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   L62-29 (LIN) - L6-11 (LIN2)	Always	Below 1 Ω
   L62-29 (LIN) - Body ground	Always	10 kΩ or higher

   TEXT IN ILLUSTRATION
   
   

   *1	Front view of wire harness connector (to Certification ECU (Smart Key ECU Assembly))
   *2	Front view of wire harness connector (to Power Management Control ECU)

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK: Go to next step 

1. Replace the power management control ECU. Refer to REMOVAL .

NEXT: Go to next step 

1. Clear the DTC. Refer to DTC CHECK / CLEAR .
2. Recheck for DTCs.

   OK

   DTC B278C is not output.

NG → See step   5 

OK → END (POWER MANAGEMENT CONTROL ECU WAS DEFECTIVE)