Lost Communication with Power Source Control (B278C)

DESCRIPTION

This DTC is stored when LIN communication between the certification ECU (smart key ECU assembly) and power management control ECU stops for more than 10 seconds.

DTC Code	DTC Detection Condition	Trouble Area
B278C	No communication between the certification ECU (smart key ECU assembly) and power management control ECU for more than 10 seconds.	Power management control ECU Certification ECU (Smart key ECU assembly) Wire harness or connector AM2 fuse

WIRING DIAGRAM
CAUTION / NOTICE / HINT

NOTICE:

• If the certification ECU (smart key ECU assembly) is replaced, register the key.
• When using the Techstream to troubleshoot with the ignition switch off:

  Connect the Techstream to the DLC3, and turn the courtesy switch on and off at 1.5-second intervals until communication between the Techstream and vehicle begins.

PROCEDURE

1. CHECK HARNESS AND CONNECTOR (POWER MANAGEMENT CONTROL ECU - BATTERY AND BODY GROUND)

(a) Disconnect the D43 ECU connector.

(b) Measure the resistance and voltage according to the value(s) in the table below.

Standard Resistance:

Tester Connection	Condition	Specified Condition
D43-5 (GND2) - Body ground	Always	Below 1 Ω
D43-6 (GND) - Body ground	Always	Below 1 Ω

Standard Voltage:

Tester Connection	Condition	Specified Condition
D43-1 (AM22) - Body ground	Always	11 to 14 V
D43-2 (AM21) - Body ground	Always	11 to 14 V

Text in Illustration

*1	Power Management Control ECU

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

1. CHECK HARNESS AND CONNECTOR (CERTIFICATION ECU - POWER MANAGEMENT CONTROL ECU)

(a) Disconnect the D25 ECU connector.

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
D25-29 (LIN) - D43-24 (LIN2)	Always	Below 1 Ω
D25-29 (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

1. REPLACE POWER MANAGEMENT CONTROL ECU

(a) Replace the power management control ECU (See page ).

NEXT

1. CHECK DTC OUTPUT

(a) Clear the DTC (See page ).

(b) Recheck for DTCs.

OK:

DTC B278C is not output.

OK

END (POWER MANAGEMENT CONTROL ECU WAS DEFECTIVE)

NG

REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY)