Operating Light Control Rheostat does not Change Light Brightness [11/2013 - ]: Procedure

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch on (IG) and the tester on.
3. Operate the Techstream according to the display and select "Data List". Refer to DATA LIST / ACTIVE TEST [11/2013 - ] .

   Body Electrical / Combination Meter / Data List

   Tester Display	Measurement Item/Range	Normal Condition	Diagnostic Note
   Tail Cancel SW	Tail cancel switch/ ON or OFF	ON: Headlight dimmer switch (light control switch) → TAIL or HEAD OFF: Headlight dimmer switch (light control switch) → OFF	-
   Rheostat value	Rheostat value/ Min.: 0, Max.: 100	Light control rheostat switch is dark → bright	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 PANEL fuse from the 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
   PANEL fuse	Always	Below 1 Ω

3. Reinstall the PANEL fuse.

NG → REPLACE FUSE 

OK: Go to next step 

1. Disconnect the C51 light control rheostat connector.

   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
   C51-5 (T) - Body ground	Ignition switch on (IG), light control switch on (TAIL)	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 C37 combination meter assembly connector.

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

2. Disconnect the C51 light control rheostat connector.
3. Measure the resistance according to the value(s) in the table below.

   Standard resistance

   Tester Connection	Condition	Specified Condition
   C51-5 (T) - C37-13 (ILL+)	Always	Below 1 Ω
   C51-2 (RV) - C37-6 (ILL-)	Always	Below 1 Ω
   C51-8 (TC) - C37-14 (TC)	Always	Below 1 Ω
   C51-3 (E) - Body ground	Always	Below 1 Ω
   C51-5 (T) or C37-13 (ILL+) - Body ground	Always	10 kΩ or higher
   C51-2 (RV) or C37-6 (ILL-) - Body ground	Always	10 kΩ or higher
   C51-8 (TC) or C37-14 (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.

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

2. Turn the ignition switch on (IG).
3. Using an oscilloscope, check the signal waveform of the light control rheostat.

   Item	Contents
   Terminal connection	C51-2 (RV) - Body ground
   Tool setting	5V/DIV, 50 ms /DIV
   Vehicle condition	Ignition switch on (IG)

   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