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*1, tail, head, AUTO position
- Dimmer switch in high, low or high flash (pass) position
- Fog light switch in front or off position*2
- *1: w/ DRL OFF Switch
- *2: w/ Front Fog Light
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. | 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 | - |
| Front Fog Light SW | Fog light switch front position signal | OFF or ON | OFF: Fog light switch off ON: Fog light switch in front 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 | - |
| Tester Display |
|---|
| Dimmer SW |
| Passing Light SW |
| Front Fog Light SW |
| Auto Light SW |
| Head Light SW (Head) |
| Head Light SW (Tail) |
OK:
Normal conditions listed above are displayed.
| OK | .gif) | PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE |
|
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| 2. | INSPECT HEADLIGHT DIMMER SWITCH ASSEMBLY |
(a) Remove the headlight dimmer switch assembly.
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(b) Inspect the headlight dimmer switch assembly.
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| NG | | REPLACE HEADLIGHT DIMMER SWITCH ASSEMBLY |
|
| 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 |
| J28-9 (BFG) - J8-26 (FFOG)* | 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 |
| J28-9 (BFG) or J8-26 (FFOG) - Body ground* | Always | 10 kΩ or higher |
| J28-8 (LFG) - Body ground | Always | Below 1 Ω |
| J28-15 (EL) - Body ground | Always | Below 1 Ω |
- *: w/ Front Fog Light
| OK | | REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU) |
| NG | | REPAIR OR REPLACE HARNESS OR CONNECTOR |
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Lexus RX (RX 350L, RX450h) 2016-{YEAR} Owners Manual
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Lexus RX (RX 350L, RX450h) 2016-{YEAR} Repair Manual
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