Dtc B1278 Combination Switch Ecu Communication Stop

Communication System. Lexus Gs430, Gs300. Uzs190 Grs190
Multiplex Communication. Lexus Gs430, Gs300. Uzs190 Grs190

DESCRIPTION

WIRING DIAGRAM

INSPECTION PROCEDURE

CHECK OPERATION

CHECK WIRE HARNESS (COMBINATION SWITCH ASSEMBLY (WINDSHIELD WIPER SWITCH) - BATTERY AND BODY GROUND)

CHECK RESISTANCE OF COMMUNICATION LINE

DTC B1278 Combination Switch ECU Communication Stop


DESCRIPTION

This DTC is detected when communication between the combination switch (windshield wiper switch) and network gateway ECU stops for more than 10 seconds.

DTC No.
DTC Detection Condition
Trouble Area
B1278
Combination switch ECU communication stops
  1. Combination switch assembly (windshield wiper switch)
  2. Wire harness

WIRING DIAGRAM


Lexus Gs430, Gs300. Uzs190 Grs190.Multiplex Communication.Multiplex Communication System. Dtc B1278 Combination Switch Ecu Communication Stop


INSPECTION PROCEDURE

1.CHECK OPERATION

  1. Check that the windshield wiper switch can operate the wipers normally.

    OK:
    Windshield wiper switch can operate wipers normally.


NG
Go to step 2
OK

REPLACE WINDSHIELD WIPER SWITCH ASSEMBLY

2.CHECK WIRE HARNESS (COMBINATION SWITCH ASSEMBLY (WINDSHIELD WIPER SWITCH) - BATTERY AND BODY GROUND)
Lexus Gs430, Gs300. Uzs190 Grs190.Multiplex Communication.Multiplex Communication System. Dtc B1278 Combination Switch Ecu Communication Stop

  1. Disconnect the L22 combination switch connector.

  1. Measure the resistance and voltage of the wire harness side connector.

    Standard Resistance:
    Tester Connection
    		Specified Condition
    L22-5 (E) - Body ground
    		Below 1 Ω
    Standard Voltage:
    Tester Connection
    		Specified Condition
    L22-1 (B) - Body ground
    		10 to 14 V


NG
REPAIR OR REPLACE HARNESS AND CONNECTOR
OK


3.CHECK RESISTANCE OF COMMUNICATION LINE

Lexus Gs430, Gs300. Uzs190 Grs190.Multiplex Communication.Multiplex Communication System. Dtc B1278 Combination Switch Ecu Communication Stop

  1. Disconnect the L22 switch connector.

  1. Disconnect the L68 ECU and 2F Front Controller ECU connectors.

  1. Measure the resistance of the wire harness side connectors.

    Standard resistance:
    Tester Connection
    		Specified Condition
    L22-6 (MPX1) - L68-21 (MPX2)
    		Below 1 Ω
    L22-7 (MPX2) - 2F-5 (MPX1)
    		Below 1 Ω
    Result:
    Result
    		Proceed to
    Both are OK
    		A
    One is OK
    		B
    Both are NG
    		C


B
REPLACE WINDSHIELD WIPER SWITCH ASSEMBLY AND HARNESS AND CONNECTOR

C
REPAIR OR REPLACE HARNESS AND CONNECTOR
A

REPLACE COMBINATION SWITCH ASSEMBLY (WINDSHIELD WIPER SWITCH ASSEMBLY)