Lexus NX: Theft Warning Siren Circuit

Lexus NX Service Manual / Vehicle Interior / Theft Deterrent / Keyless Entry / Theft Deterrent System / Theft Warning Siren Circuit

DESCRIPTION

The theft warning siren has an internal battery. If the vehicle auxiliary battery cable is disconnected or any of the communication lines are open, the theft warning siren detects this and sounds its siren.

Although the theft warning siren usually sounds by receiving a signal from the main body ECU (multiplex network body ECU), the theft warning siren can sound by its internal battery in case the vehicle auxiliary battery cable is disconnected.

The main body ECU (multiplex network body ECU) sends an arming signal to the theft warning siren while transferring to the armed state, and it also sends a disarming signal to the siren while switching to the disarmed state. Also, the main body ECU (multiplex network body ECU) can cause the theft warning siren to sound by sending an alarm signal during the alarm sounding state.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

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

1.	PERFORM ACTIVE TEST USING TECHSTREAM (SECURITY HORN2)

(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) According to the display on the Techstream, perform the Active Test.

Body Electrical > Main Body > Active Test

Tester Display	Measurement Item	Control Range	Diagnostic Note
Security Horn2	Theft warning siren assembly	ON or OFF	-

Body Electrical > Main Body > Active Test

Tester Display
Security Horn2

OK:

The theft warning siren assembly sounds and stops correctly when operated through the Techstream.

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

2.	CHECK HARNESS AND CONNECTOR (THEFT WARNING SIREN ASSEMBLY - BATTERY AND BODY GROUND)

(a) Disconnect the theft warning siren assembly connector.

*a	Front view of wire harness connector (to Theft Warning Siren Assembly)

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

Standard Voltage:

Tester Connection	Switch Condition	Specified Condition
P50-3 (+B) - Body ground	Power switch off	11 to 14 V

Standard Resistance:

Tester Connection	Condition	Specified Condition
P50-1 (GND) - Body ground	Always	Below 1 Ω

REPAIR OR REPLACE HARNESS OR CONNECTOR

3.	CHECK HARNESS AND CONNECTOR (THEFT WARNING SIREN ASSEMBLY - MAIN BODY ECU [MULTIPLEX NETWORK BODY ECU])

(a) Disconnect the P50 theft warning siren assembly connector.

(b) Disconnect the I47 main body ECU (multiplex network body ECU) connector.

Standard Resistance:

Tester Connection	Condition	Specified Condition
P50-2 (CONT) - I47-18 (SSCL)	Always	Below 1 Ω
P50-2 (CONT) - Body ground	Always	10 kΩ or higher
I47-18 (SSCL) - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

4.	CHECK THEFT WARNING SIREN ASSEMBLY

(a) Temporarily replace the theft warning siren assembly with a new or normally functioning one.

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(b) Check the operation of the theft warning siren assembly function.

OK:

Theft warning siren assembly function operates normally.

END (THEFT WARNING SIREN ASSEMBLY WAS DEFECTIVE)

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

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