Operating Light Control Rheostat does not Change Light Brightness: Procedure

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON.
3. Turn the Techstream on.
4. Enter the following menus: Body Electrical / Combination Meter / Data List.
5. According to the display on the Techstream, read the Data List.
   COMBINATION METER
   
   

   Tester Display	Measurement Item/Range	Normal Condition	Diagnostic Note
   Tail Cancel SW	Tail cancel switch OFF or ON	OFF: Headlight dimmer switch (Light control switch) → TAIL or HEAD ON: Headlight dimmer switch (Light control switch) → OFF	-
   Rheostat value	Rheostat value Min.: 0 Max.: 100	Light control rheostat switch is dark (0) → bright (100)	Unit: %

   OK

   Light brightness can be changed within the specified range by actual operation.

NG → See step   2 

OK → See step   6 

1. Remove the PANEL1 fuse from the main body ECU.
   Fig 1: Identifying PANEL1 Fuse In Main Body ECU

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Measure the resistance according to the value in the table below.

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   PANEL1 fuse	Always	Below 1 Ω

3. Reinstall the PANEL1 fuse.

NG → REPLACE FUSE 

OK: Go to next step 

1. Disconnect the F28 light control rheostat connector.
   Fig 2: Identifying F28 Light Control Rheostat Connector Terminals

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Measure the voltage according to the value in the table below.

   Standard Voltage

   Tester Connection	Switch Condition	Specified Condition
   F28-5 (T) - Body ground	Ignition switch ON, light control switch on (TAIL or HEAD)	11 to 14 V

3. Reconnect the light control rheostat connector.

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK: Go to next step 

1. Disconnect the F2 combination meter assembly connector.
   Fig 3: Identifying F2 Combination Meter Assembly Connector Terminals

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Disconnect the F28 light control rheostat connector.
3. Measure the resistance according to the value(s) in the table below.

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   F28-5 (T) - F2-7 (ILL+)	Always	Below 1 Ω
   F28-2 (RV) - F2-6 (ILL-)	Always	Below 1 Ω
   F28-8 (TC) - F2-8 (TC)	Always	Below 1 Ω
   F28-3 (E) - Body ground	Always	Below 1 Ω
   F28-5 (T) or F2-7 (ILL+) - Body ground	Always	10 kΩ or higher
   30-2 (RV) or F2-6 (ILL-) - Body ground	Always	10 kΩ or higher
   F28-8 (TC) or F2-8 (TC) - Body ground	Always	10 kΩ or higher

4. Reconnect the combination meter assembly connector.
5. Reconnect the light control rheostat connector.

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK: Go to next step 

1. Remove the light control rheostat but without disconnecting the connector.
   Fig 4: Identifying F28 Connector Terminals And Waveform Graph

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Turn the ignition switch to ON.
3. Using an oscilloscope, check the signal waveform of the light control rheostat.

   Item	Contents
   Terminal connection	F28-2 (RV) - Body ground
   Tool setting	5V/DIV, 50 ms /DIV
   Vehicle condition	Ignition switch ON

   OK

   Waveform is as shown in the illustration.

   HINT: 

   Duty ratio changes as the illumination dims. (A becomes longer)

4. Reinstall the light control rheostat.

NG → See step   7 

OK → See step   8