Operating Light Control Rheostat does not Change Light Brightness: Procedure

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch ON and turn the tester ON.
3. Select the item below in the Data List, and read the value displayed on the Techstream.

   Body Electrical / Combination Meter / Data List:

   Tester Display	Measurement Item/Range	Normal Condition	Diagnostic Note
   Rheostat value (A/D)	Rheostat value Min.: 0 Max.: 255	Light control rheostat switch is Dark (0)→Bright (255)	-

   OK

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

NG → See step   2 

OK → REPLACE COMBINATION METER ASSEMBLY 

1. Remove the GAUGE fuse from the main body ECU.
2. Measure the resistance.

   OK

   Below 1 Ω

3. Reinstall the GAUGE fuse.

NG → REPLACE FUSE 

OK: Go to next step 

1. Disconnect the D29 light control rheostat connector.
   Fig 1: Identifying D29 Light Control Rheostat Connector

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Measure the voltage.

   Standard voltage

   Tester Connection	Condition	Specified Condition
   D29-10 - Body ground	Ignition switch ON	11 to 14V

3. Reconnect the light control rheostat connector.

OK → See step   5 

NG: Go to next step 

1. Disconnect the D29 light control rheostat connector.
   Fig 2: Identifying 4P Main Body ECU Connector

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Disconnect the 4P main body ECU connector.
3. Measure the resistance.

   Standard resistance

   Tester	Condition	Specified Condition
   D29-10 (IG)- 4P-1	Always	Below 1 Ω

4. Reconnect the light control rheostat connector.
5. Reconnect the main body ECU connector.

NG → REPLACE MAIN BODY ECU 

OK: Go to next step 

1. Remove the light control rheostat but without disconnecting the connector.
   Fig 3: Identifying Light Control Rheostat

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

   Item	Contents
   Terminal connection	D29-2 (RV) - Body ground
   Tool setting	5V / DIV, 50ms / 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   8 

OK: Go to next step 

1. Disconnect the D1 combination meter assembly connector.
   Fig 4: Identifying D1 Combination Meter Assembly And D29 Light Control Rheostat Connectors

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Disconnect the D29 light control rheostat connector.
3. Measure the resistance.

   Standard resistance

   Tester Connection	Specified Condition
   D1-7 (ILL-) - D29-2 (RV)	Below 1 Ω

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

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK → See step   7