Dtc B1278 Combination Switch Ecu Communication Stop

Communication System. Lexus Is250, Is220D. Gse20 Ale20
Multiplex Communication. Lexus Is250, Is220D. Gse20 Ale20

DESCRIPTION

WIRING DIAGRAM

INSPECTION PROCEDURE

INSPECT FUSE (ECU-IG RH, MPX-B)

CHECK WIRE HARNESS (COMBINATION SWITCH ASSEMBLY - 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 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 Is250, Is220D. Gse20 Ale20.Multiplex Communication.Multiplex Communication System. Dtc B1278 Combination Switch Ecu Communication Stop


INSPECTION PROCEDURE

HINT:
When "+B of GND short malfunction of communication bus" DTCs (B1214 and B1215) are detected at the same time as "communication stop" DTC B1278, repair the "+B or GND short malfunction of communication bus" DTCs first.
1.INSPECT FUSE (ECU-IG RH, MPX-B)

  1. Remove the ECU-IG RH fuse from the main body ECU RH (cowl side J/B RH).

  1. Remove the MPX-B fuse from the engine room J/B No. 1.

    Standard resistance:
    Below 1 Ω


NG
REPLACE FUSE
OK


2.CHECK WIRE HARNESS (COMBINATION SWITCH ASSEMBLY - BATTERY AND BODY GROUND)


    Lexus Is250, Is220D. Gse20 Ale20.Multiplex Communication.Multiplex Communication System. Dtc B1278 Combination Switch Ecu Communication Stop

  1. Disconnect the J26 ECU connector.

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

    Standard voltage:
    Tester Connection
    		Condition
    		Specified Condition
    B (J26-1) - Body ground
    		Always
    		10 to 14 V
    IG (J26-2) - Body ground
    		Engine switch on (IG)
    		10 to 14 V
    Standard resistance:
    Tester Connection
    		Specified Condition
    E (J26-5) - Body ground
    		Below 1 Ω


NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
OK


3.CHECK RESISTANCE OF COMMUNICATION LINE


    Lexus Is250, Is220D. Gse20 Ale20.Multiplex Communication.Multiplex Communication System. Dtc B1278 Combination Switch Ecu Communication Stop

  1. Disconnect the J26, J76 and J55 ECU connectors.

  1. Measure the resistance between the specified terminals on the wire harness side connectors.

    Standard resistance:
    Tester Connection
    		Specified Condition
    MPX1 (J26-6) - MPD2 (J76-12)
    		Below 1 Ω
    MPX2 (J26-7) - MPX1 (J55-7)
    		Below 1 Ω
    Result:
    Result
    		Proceed to
    Both are OK
    		A
    One is OK
    		B
    Both are NG
    		C


B
REPAIR OR REPLACE HARNESS OR CONNECTOR AND REPLACE COMBINATION SWITCH ASSEMBLY

C
REPAIR OR REPLACE HARNESS OR CONNECTOR
A

REPLACE COMBINATION SWITCH ASSEMBLY