DTC B1278: Combination Switch ECU Communication Stop: Procedure

WARNING: This page is about a different car, the 2011 Toyota Avalon. However, it is still accessible from the selected car via links, so may be relevant.

CHECK HARNESS AND CONNECTOR (COMBINATION SWITCH - BATTERY AND BODY GROUND)

Disconnect the D13 combination switch connector.

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

Voltage

Tester Connection	Condition	Specified Condition
D13-1 (B) - Body ground	Always	10 to 14 V
D13-2 (IG) - Body ground	Ignition switch off→ on (IG)	0 V → 10 to 14 V

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

Resistance

Tester Connection	Condition	Specified Condition
D13-5 (E) - Body ground	Always	Below 1 Ω

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR

OK: Go to next step

CHECK RESISTANCE OF COMMUNICATION LINE

Disconnect the D13, D6, and D39^*1 or D37^*2 ECU connectors.

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

Resistance

Tester Connection	Condition	Specified Condition
D13-6 (MPX1) - D6-21 (MPX2)	Always	Below 1 Ω
D13-7 (MPX2) - D39-27 (MPX1) ^*1		Below 1 Ω
D13-7 (MPX2) - D37-30 (MPX+) ^*2		Below 1 Ω

HINT:

^*1 : w/ Smart key system

^*2 : w/o Smart key system

Result

Result	Proceed to
Both are OK	A
One is OK	B
Both are NG	C

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

C → REPAIR OR REPLACE HARNESS OR CONNECTOR

A → REPLACE COMBINATION SWITCH