DTC B1278: Combination Switch ECU Communication Stop: Procedure

1. Remove the ECU-IG RH fuse from the cowl side J/B RH.
2. Remove the MPX-B fuse from the engine room J/B No. 1.

   Standard resistance

   Below 1 Ω

NG → REPLACE FUSE 

OK: Go to next step 

1. Disconnect the J26 ECU connector.

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

2. 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: Go to next step 

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

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

2. 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