Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual: Lost Communication with Wiper System LIN BUS (B1373)

DESCRIPTION

The main body ECU (multiplex network body ECU) communicates with the windshield wiper motor and link assembly (wiper ECU), windshield wiper switch assembly and rain sensor via LIN communication. If a malfunction occurs in the LIN communication line and a communication error occurs, this DTC is stored.

DTC No.	Detection Item	DTC Detection Condition	Trouble Area	Memory	DTC Output from
B1373	Lost Communication with Wiper System LIN BUS	When the battery voltage is 9.5 V or more, a malfunction in the communication or LIN communication line between the main body ECU (multiplex network body ECU) and components of the wiper system occurs for 7 seconds or more 3 times consecutively.	Front wiper motor and link assembly Windshield wiper switch assembly Rain sensor Harness or connector Main body ECU (multiplex network body ECU)	○	Main body ECU (multiplex network body ECU)

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

Before replacing the main body ECU (multiplex network body ECU), refer to Service Bulletin.

PROCEDURE

1.	CHECK HARNESS AND CONNECTOR (MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU) - FRONT WIPER MOTOR AND LINK ASSEMBLY)

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

(b) Disconnect the i1 front wiper motor and link assembly connector.

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

(d) Disconnect the U3 rain sensor connector (w/ Auto Wiper System).

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
J9-8 (LIN3) - i1-2 (MPX1)	Always	Below 1 Ω
J9-8 (LIN3) - J31-7 (MPX1)	Always	Below 1 Ω
J9-8 (LIN3) - U3-3 (MPX) *	Always	Below 1 Ω
J9-8 (LIN3) or i1-2 (MPX1) or J31-7 (MPX1) - Body ground	Always	10 kΩ or higher
J9-8 (LIN3) or i1-2 (MPX1) or J31-7 (MPX1) or U3-3 (MPX) - Body ground *	Always	10 kΩ or higher

NG

GO TO STEP 5

OK

2.	CHECK FRONT WIPER MOTOR AND LINK ASSEMBLY

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

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

(c) Reconnect the U3 rain sensor connector (w/ Auto Wiper System).

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

(e) Check for DTCs.

Click here

Body Electrical > Main Body > Trouble Codes

Result	Proceed to
DTC B1373 is not output.	A
DTC B1373 is output.	B

A

REPLACE FRONT WIPER MOTOR AND LINK ASSEMBLY

B

3.	CHECK WINDSHIELD WIPER SWITCH ASSEMBLY

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

(b) Reconnect the i1 front wiper motor and link assembly connector.

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

(d) Check for DTCs.

Click here

Body Electrical > Main Body > Trouble Codes

Result	Proceed to
DTC B1373 is not output.	A
DTC B1373 is output (w/o Auto Wiper System).	B
DTC B1373 is output (w/ Auto Wiper System).	C

A

REPLACE WINDSHIELD WIPER SWITCH ASSEMBLY

B

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

C

4.	CHECK RAIN SENSOR

(a) Disconnect the U3 rain sensor connector.

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

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

(d) Check for DTCs.

Click here

Body Electrical > Main Body > Trouble Codes

Result	Proceed to
DTC B1373 is not output.	A
DTC B1373 is output.	B

A

REPLACE RAIN SENSOR

B

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

5.	CHECK WIPER MOTOR WIRE

(a) Remove the wiper motor wire.

Click here

(b) Measure the resistance according to the value(s) in the table below. Standard Resistance: Tester Connection Condition Specified Condition i1-2 (MPX1) - iA1-1 Always Below 1 Ω

*a Front view of wire harness connector (to Front Wiper Motor and Link Assembly) *b Front view of wire harness connector (to Wire Harness)

OK

REPAIR OR REPLACE HARNESS OR CONNECTOR

NG

REPLACE WIPER MOTOR WIRE