Toyota Avalon (XX50) 2019-2022 Service & Repair Manual: Taillight Relay Circuit

DESCRIPTION

The main body ECU (multiplex network body ECU) controls the operation of the TAIL relay.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

Inspect the fuses for circuits related to this system before performing the following procedure.
Before replacing the main body ECU (multiplex network body ECU), refer to Registration.
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PROCEDURE

1.	PERFORM ACTIVE TEST USING TECHSTREAM

(a) Connect the Techstream to the DLC3.

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

(d) Enter the following menus: Body Electrical / Main Body / Active Test.

(e) Perform the Active Test according to the display on the Techstream.

Body Electrical > Main Body > Active Test

Tester Display	Measurement Item	Control Range	Diagnostic Note
Taillight Relay	Taillight relay	OFF or ON	-

Body Electrical > Main Body > Active Test

Tester Display
Taillight Relay

OK:

Taillights illuminate.

PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE

2.	CHECK HARNESS AND CONNECTOR (POWER SOURCE - INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY)

(a) Disconnect the 4K instrument panel junction block assembly connector.

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

Standard Voltage:

Tester Connection	Condition	Specified Condition
4K-1 - Body ground	Power switch off	11 to 14 V

REPAIR OR REPLACE HARNESS OR CONNECTOR

3.	INSPECT INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY

Component without harness connected

(Instrument Panel Junction Block Assembly)

(a) Remove the main body ECU (multiplex network body ECU) from the instrument panel junction block assembly.

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(b) Connect a positive (+) lead from the auxiliary battery to terminal 4K-1.

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

Standard Voltage:

Tester Connection	Condition	Specified Condition
4F-32 - Auxiliary battery negative (-) terminal	Always	11 to 14 V
4H-30 - Auxiliary battery negative (-) terminal	Always	11 to 14 V

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

REPLACE INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY

Toyota Avalon (XX50) 2019-2022 Service & Repair Manual > Seat Belt Warning System(for Gasoline Model): Rear Seat Belt Warning Light Malfunction
DESCRIPTION The main body ECU (multiplex network body ECU) detects whether either the rear doors are open or closed based on the courtesy light switch condition and then sends the rear door status signal to the combination meter assembly. The combination meter assembly detects rear seat belt state. ...

Toyota Avalon (XX50) 2019-2022 Owners Manual