Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSTOYOTA2004CELICA GT, STANDARDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 134 (INSTRUMENT PANEL)SYSTEM TESTSTEST E: OPERATING LIGHT CONTROL RHEOSTAT DOES NOT CHANGE LIGHT BRIGHTNESS
2004 Toyota Celica GT, Standard
Test E: Operating Light Control Rheostat Does Not Change Light Brightness
2004 Toyota Celica GT, StandardSECTION Test E: Operating Light Control Rheostat Does Not Change Light Brightness
WARNING: This page is about a different car, the 2003 Lexus ES 300 and 2002 Lexus ES 300. However, it is still accessible from the selected car via links, so may be relevant.
- Check illumination:
- Operate the rheostat and check that the quantity of light for the combination meter assembly, audio system and A/C control panel etc. are normally changed. See Fig 1.
- If all lights do not change, go to the next step. If the combination meter does not change, check and replace the combination meter assembly. See COMBINATION METER SAFETY PAD SUB-ASSEMBLYΒ under REMOVAL & INSTALLATION.
- Check the combination meter assembly:
- Remove the combination meter assembly with the connectors still connected. Turn the ignition switch ON. Measure the voltage (0.1-4.1 volts) between terminals No. C8-1 and C8-19 of the combination meter assembly connector. See Figure.
- If the voltage is OK, go to the next step. If the voltage is not OK, check and replace the combination meter assembly. See COMBINATION METER SAFETY PAD SUB-ASSEMBLYΒ under REMOVAL & INSTALLATION.
- Inspect the light control rheostat:
- Check the continuity between terminals No. 1 (TC) and 3 (T) of the light control rheostat when the light control rheostat operation. See LIGHT CONTROL RHEOSTAT OPERATIONΒ table. See CONNECTOR IDENTIFICATIONΒ .LIGHT CONTROL RHEOSTAT OPERATION
Switch Position Terminal (Symbol) Continuity Most Brighten Position 1 (TC) To 3 (T) No Continuity Except Most Brighten Position 1 (TC) To 3 (T) Continuity - Check the light control rheostat resistance. Measure the resistance (approximately 10 kΞ©) between terminals No. 1 (TC) and 3 (T) of the light control rheostat. Measure the resistance between terminals No. 1 (TC) and 4 (RV) of the light control rheostat when operating the light control rheostat. Check that the resistance value changes continuously. See LIGHT CONTROL RHEOSTAT STANDARD RESISTANCEΒ table.LIGHT CONTROL RHEOSTAT STANDARD RESISTANCE
Condition Resistance Turned To Brightest Position Approximately 10 k Ohms Other Conditions Than Above Change Between 0-10 k Ohms - If the resistance is OK, go to the next step. If the resistance is not OK, replace the light control rheostat.
- Check the continuity between terminals No. 1 (TC) and 3 (T) of the light control rheostat when the light control rheostat operation. See LIGHT CONTROL RHEOSTAT OPERATIONΒ table. See CONNECTOR IDENTIFICATIONΒ .
- Check the harness and connector. If the results are OK, check and replace the multiplex network body ECU. See MULTIPLEX COMMUNICATION SYSTEMS article in COMMUNICATION DEVICES. If the results are not OK, repair or replace the harness or connector.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- β’ You smell fuel, burning insulation, or see smoke.
- β’ Brakes feel soft, pull hard to one side, or make grinding noises.
- β’ The engine overheats, stalls repeatedly, or misfires under load.
- β’ You are missing required tools, torque specs, or safe lifting equipment.
- β’ You are not confident in the next step or safety outcome.