DTC B1271 Combination Meter ECU Communication Stop

DESCRIPTION

This DTC is detected when communication between the combination meter ECU and gateway ECU stops for more than 10 seconds.

DTC No.	DTC Detection Condition	Trouble Area
B1271	Combination meter ECU communication stops	Combination meter ECU Wire harness

Dtc B1271 Combination Meter Ecu Communication Stop. MULTIPLEX COMMUNICATION. Lexus IS250 IS220d GSE20 ALE20

When "+B of GND short malfunction of communication bus" DTCs (B1266 and B1267) are detected at the same time as "communication stop" DTC B1271, repair the "+B or GND short malfunction of communication bus" DTCs first.

1.INSPECT FUSE (DOME, MPX-B)

Remove the DOME and MPX-B fuses from the engine room J/B No. 1.

Measure the resistance of the fuses.

REPLACE FUSE

OK

2.CHECK WIRE HARNESS (COMBINATION METER ECU - BATTERY AND BODY GROUND)

Disconnect the J34 ECU connector.

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

Standard voltage:
Tester Connection Condition Specified Condition
B (J34-23) - Body ground Always 10 to 14 V
B (J34-24) - Body ground Always 10 to 14 V

Standard resistance:
Tester Connection Specified Condition
E2 (J34-1) - Body ground Below 1 Ω
ES (J34-13) - Body ground Below 1 Ω

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

3.CHECK RESISTANCE OF COMMUNICATION LINE

Disconnect the J34, J76, A27 and J58 ECU connectors.

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

Standard resistance:
Tester Connection Specified Condition
MPX- (J34-18) - MPI1 (J76-4) Below 1 Ω
^*1MPX+ (J34-6) - MPX2 (A27-6) Below 1 Ω
^*2MPX+ (J34-6) - MPX- (J58-31) Below 1 Ω

*1: w/ Adaptive front-lighting system

*2: w/o Adaptive front-lighting system

REPLACE COMBINATION METER ECU AND REPAIR OR REPLACE HARNESS OR CONNECTOR

REPAIR OR REPLACE HARNESS OR CONNECTOR

REPLACE COMBINATION METER ECU