Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual: Lost Communication with Combination Switch ECU (B1278)

Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual / Vehicle Exterior / Wiper / Washer / Wiper And Washer System / Lost Communication with Combination Switch ECU (B1278)

DESCRIPTION

The main body ECU (multiplex network body ECU) and windshield wiper switch assembly communicate via LIN communication. The main body ECU (multiplex network body ECU) stores this DTC if communication becomes abnormal.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

Memory

DTC Output from

B1278

Lost Communication with Combination Switch ECU

When the battery voltage is 9.5 V or more, a communication malfunction between the main body ECU (multiplex network body ECU) and windshield wiper switch assembly is detected for 10 seconds or more.
  • Windshield wiper switch assembly
  • Harness or connector
  • Main body ECU (multiplex network body ECU)

○

Main body ECU (multiplex network body ECU)

WIRING DIAGRAM

PROCEDURE

1.

CLEAR DTC

(a) Clear the DTCs.

Click here

Body Electrical > Main Body > Clear DTCs
NEXT

2.

CHECK FOR DTC

(a) Turn the engine switch on (IG).

(b) Check for DTCs.

Click here

Body Electrical > Main Body > Trouble Codes

Result

Proceed to

DTC B1278 is not output.

A

DTC B1278 is output.

B
A

USE SIMULATION METHOD TO CHECK

B

3.

CHECK HARNESS AND CONNECTOR (MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU) - WINDSHIELD WIPER SWITCH ASSEMBLY)

(a) Disconnect the J9 main body ECU (multiplex network body ECU) connector.

(b) Disconnect the J31 windshield wiper switch assembly connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

J9-8 (LIN3) - J31-7 (MPX1)

Always

Below 1 Ω

J9-8 (LIN3) or J31-7 (MPX1) - Body ground

Always

10 kΩ or higher
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

4.

CHECK HARNESS AND CONNECTOR (FRONT WIPER MOTOR AND LINK ASSEMBLY - POWER SOURCE)

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

Standard Voltage:

Tester Connection

Condition

Specified Condition

J31-10 (+B2) - Body ground

Engine switch off

Below 1 V

Engine switch on (IG)

11 to 14 V

J31-6 (+B) - Body ground

Engine switch off

Below 1 V

Engine switch on (IG)

11 to 14 V
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

5.

CHECK HARNESS AND CONNECTOR (WINDSHIELD WIPER SWITCH ASSEMBLY - BODY GROUND)

(a) Disconnect the J33 windshield wiper switch assembly connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

J31-8 (E) - Body ground

Always

Below 1 Ω

J33-4 (EW) - Body ground

Always

Below 1 Ω
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

6.

REPLACE WINDSHIELD WIPER SWITCH ASSEMBLY

(a) Replace the windshield wiper switch assembly with a new or known good one.

Click here

(b) Turn the engine switch on (IG).

(c) Check for DTCs.

Click here

Body Electrical > Main Body > Trouble Codes

Result

Proceed to

DTC B1278 is not output.

A

DTC B1278 is output.

B
A

END
B

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

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