Lexus RX (RX 350L, RX450h) 2016-2026 Repair Manual: Light Sensor Circuit (B1244)

DESCRIPTION

The automatic light control sensor detects ambient light. The sensor creates an electrical signal based on the amount of light detected, and sends the signal to the main body ECU (multiplex network body ECU). The main body ECU (multiplex network body ECU) turns on or off the headlights and taillights according to the signal.

DTC No.	Detection Item	DTC Detection Condition	Trouble Area	DTC Output from
B1244	Light Sensor Circuit	The engine switch is on (IG). Either of the following conditions is met: Malfunction in automatic light control sensor Open or short in automatic light control sensor circuit 5 seconds or more	Automatic light control sensor Harness or connector Main body ECU (multiplex network body ECU)	Main Body

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

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

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PROCEDURE

1.

CLEAR DTC

(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 / Trouble Codes.

(e) Clear the DTCs.

Body Electrical > Main Body > Clear DTCs

NEXT

2.	CHECK FOR DTC

(a) Connect the Techstream to the DLC3.

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

(c) Wait 10 seconds or more.

(d) Turn the Techstream on.

(e) Enter the following menus: Body Electrical / Main Body / Trouble Codes.

(f) Check for DTCs.

Body Electrical > Main Body > Trouble Codes

OK:

DTC B1244 is not output.

OK

USE SIMULATION METHOD TO CHECK

NG

3.	READ VALUE USING TECHSTREAM

(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 / Data List.

(e) According to the display on the Techstream, read the Data List and check that the value of Light Sensor Illuminance changes while performing the following:

(1) Cover the automatic light control sensor with an opaque object.

(2) Slowly move the opaque object to uncover and then cover the automatic light control sensor.

Body Electrical > Main Body > Data List

Tester Display	Measurement Item	Range	Normal Condition	Diagnostic Note
Light Sensor Illuminance	Light control sensor illuminance	0 to 8191 lx or SensorFail	Value is output according to ambient light level	The displayed value is "0" when no light is detected.

Body Electrical > Main Body > Data List

Tester Display
Light Sensor Illuminance

OK:

The value changes according to the amount the automatic light control sensor is covered.

OK

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

NG

4.	CHECK HARNESS AND CONNECTOR (AUTOMATIC LIGHT CONTROL SENSOR - MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU))

(a) Disconnect the K3 automatic light control sensor connector.

(b) Disconnect the J8 main body ECU (multiplex network body ECU) connector.

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
K3-1 (CLTB) - J8-19 (CLTB)	Always	Below 1 Ω
K3-4 (CLTS) - J8-20 (CLTS)	Always	Below 1 Ω
K3-2 (CLTE) - J8-21 (CLTE)	Always	Below 1 Ω
K3-1 (CLTB) or J8-19 (CLTB) - Body ground	Always	10 kΩ or higher
K3-4 (CLTS) or J8-20 (CLTS) - Body ground	Always	10 kΩ or higher
K3-2 (CLTE) or J8-21 (CLTE) - Body ground	Always	10 kΩ or higher

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

5.	INSPECT MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

*a	Component with harness connected (Main Body ECU (Multiplex Network Body ECU))

(a) Connect the J8 main body ECU (multiplex network body ECU) connector.

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

Standard Voltage:

Tester Connection	Condition	Specified Condition
J8-19 (CLTB) - J8-21 (CLTE)	Engine switch off	Below 1 V
	Engine switch on (IG)	11 to 14 V

NG

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

OK

6.	INSPECT AUTOMATIC LIGHT CONTROL SENSOR

(a) Inspect the automatic light control sensor.

Click here

OK

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

NG

REPLACE AUTOMATIC LIGHT CONTROL SENSOR