Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual: Security Horn Circuit

Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual / Vehicle Interior / Theft Deterrent / Keyless Entry / Theft Deterrent System / Security Horn Circuit

DESCRIPTION

When the theft deterrent system is switched from the armed state to the alarm sounding state, the main body ECU (multiplex network body ECU) transmits a signal to cause the security horn assembly to sound at intervals of 0.4 seconds.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

  • Before replacing the main body ECU (multiplex network body ECU), refer to Registration.

    Click here

  • Inspect the fuses for circuits related to this system before performing the following procedure.

PROCEDURE

1.

PERFORM ACTIVE TEST USING TECHSTREAM (SECURITY HORN)

(a) Connect the Techstream to the DLC3.

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

(c) Turn the Techstream on.

(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

Security Horn

Security horn Assembly

OFF/ON

-
Body Electrical > Main Body > Active Test

Tester Display

Security Horn

OK:

The security horn assembly sounds and stops correctly when operated through the Techstream.

OK

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

NG

2.

INSPECT SECURITY HORN ASSEMBLY

(a) Remove the security horn assembly.

Click here

(b) Inspect the security horn assembly.

Click here

NG

REPLACE SECURITY HORN ASSEMBLY

OK

3.

INSPECT S-HORN RELAY

(a) Remove the S-HORN relay from the engine room relay block.

*1

S-HORN Relay

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

3 - 5

Battery voltage not applied between terminals 1 and 2

10 kΩ or higher

3 - 5

Battery voltage applied between terminals 1 and 2

Below 1 Ω
NG

REPLACE S-HORN RELAY
OK

4.

INSPECT INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY

(a) Remove the main body ECU (multiplex network body ECU).

Click here

*a

Component without harness connected

(Instrument Panel Junction Block Assembly)

-

-

(b) Disconnect the 2C instrument panel junction block assembly connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

2C-26 - MB-29 (SH)

Always

Below 1 Ω
NG

REPLACE INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY

OK

5.

CHECK HARNESS AND CONNECTOR (BATTERY - S-HORN RELAY)

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

Standard Voltage:

Tester Connection

Condition

Specified Condition

Engine room relay block and junction block assembly S-HORN relay terminal 1 - Body ground

Always

11 to 14 V

Engine room relay block and junction block assembly S-HORN relay terminal 5 - Body ground

Always

11 to 14 V

*1

Engine Room Relay Block and Junction Block Assembly
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

6.

CHECK HARNESS AND CONNECTOR (S-HORN RELAY - SECURITY HORN ASSEMBLY)

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

Engine room relay block and junction block assembly S-HORN relay terminal 3 - A10-1

Always

Below 1 Ω

Engine room relay block and junction block assembly S-HORN relay terminal 3 or A10-1 - Body ground

Always

10 kΩ or higher

*1

Engine Room Relay Block and Junction Block Assembly
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

7.

CHECK HARNESS AND CONNECTOR (S-HORN RELAY - INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY)

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

Engine room relay block and junction block assembly S-HORN relay terminal 2 - 2C-26

Always

Below 1 Ω

Engine room relay block and junction block assembly S-HORN relay terminal 2 or 2C-26 - Body ground

Always

10 kΩ or higher

*1

Engine Room Relay Block and Junction Block Assembly
OK

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
    Horn Circuit
    DESCRIPTION When the theft deterrent system is switched from the armed state to the alarm sounding state, the main body ECU (multiplex network body ECU) transmits a signal to cause the horns to sound ...

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