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	Combination switch assembly (windshield wiper switch) Wire harness

Dtc B1278 Combination Switch Ecu Communication Stop. MULTIPLEX COMMUNICATION. Lexus IS250 IS220d GSE20 ALE20

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)

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

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

REPLACE FUSE

OK

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

Disconnect the J26 ECU connector.

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

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

3.CHECK RESISTANCE OF COMMUNICATION LINE

Disconnect the J26, J76 and J55 ECU connectors.

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

REPAIR OR REPLACE HARNESS OR CONNECTOR AND REPLACE COMBINATION SWITCH ASSEMBLY

REPAIR OR REPLACE HARNESS OR CONNECTOR

REPLACE COMBINATION SWITCH ASSEMBLY

Tester Connection	Specified Condition
E (J26-5) - Body ground	Below 1 Ω