Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual: Headlight Dimmer Switch Circuit

DESCRIPTION

The main body ECU (multiplex network body ECU) receives the following switch information:

  • Light control switch in DRL OFF*, tail, head, AUTO position
  • Dimmer switch in high, low or high flash (pass) position
  • *: w/ DRL OFF Switch

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

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

Click here

PROCEDURE

1.

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) Read the Data List according to the display on the Techstream.

Body Electrical > Main Body > Data List

Tester Display

Measurement Item

Range

Normal Condition

Diagnostic Note

Dimmer SW

Dimmer switch high position signal

OFF or ON

OFF: Dimmer switch in low position

ON: Dimmer switch in high or high flash position

-

Passing Light SW

Dimmer switch high flash position (pass) signal

OFF or ON

OFF: Dimmer switch not in high flash position

ON: Dimmer switch in high flash position

-

Auto Light SW

Light control switch AUTO position signal

OFF or ON

OFF: Light control switch not in AUTO position

ON: Light control switch in AUTO position

-

Head Light SW (Head)

Light control switch head position signal

OFF or ON

OFF: Light control switch not in head position

ON: Light control switch in head position

-

Head Light SW (Tail)

Light control switch tail position signal

OFF or ON

OFF: Light control switch not in tail or head position

ON: Light control switch in tail or head position

-

Body Electrical > Main Body > Data List

Tester Display

Dimmer SW

Passing Light SW

Auto Light SW

Head Light SW (Head)

Head Light SW (Tail)

OK:

Normal conditions listed above are displayed.

OK

PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE

NG

2.

INSPECT HEADLIGHT DIMMER SWITCH ASSEMBLY

(a) Remove the headlight dimmer switch assembly.

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(b) Inspect the headlight dimmer switch assembly.

Click here

NG

REPLACE HEADLIGHT DIMMER SWITCH ASSEMBLY

OK

3.

CHECK HARNESS AND CONNECTOR (HEADLIGHT DIMMER SWITCH ASSEMBLY - MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU) AND BODY GROUND)

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

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

J28-18 (T) - J8-22 (TAIL)

Always

Below 1 Ω

J28-19 (H) - J8-12 (HEAD)

Always

Below 1 Ω

J28-20 (A) - J8-8 (A)

Always

Below 1 Ω

J28-14 (HU) - J8-24 (HU)

Always

Below 1 Ω

J28-17 (HF) - J8-10 (HF)

Always

Below 1 Ω

J28-18 (T) or J8-22 (TAIL) - Body ground

Always

10 kΩ or higher

J28-19 (H) or J8-12 (HEAD) - Body ground

Always

10 kΩ or higher

J28-20 (A) or J8-8 (A) - Body ground

Always

10 kΩ or higher

J28-14 (HU) or J8-24 (HU) - Body ground

Always

10 kΩ or higher

J28-17 (HF) or J8-10 (HF) - Body ground

Always

10 kΩ or higher

J28-15 (EL) - Body ground

Always

Below 1 Ω

OK

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

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