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 125 (MULTIPLEX COMMUNICATION SYSTEM)TROUBLE SHOOTING
2004 Toyota Celica GT, Standard
Trouble Shooting
2004 Toyota Celica GT, StandardSECTION Trouble Shooting
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.
- Trouble shooting of a multiplex communication system complaint begins with verification of the customer problem. If problem occurs, go to step 3. If problem does not occur, go to next step.
- If problem does not occur, review conditions under which problem occurred for customer and try to duplicate those conditions. For example, if the problem occurs on rainy days or during high humidity conditions, sprinkle water onto vehicle and see if malfunction occurs. DO NOT sprinkle water directly into engine compartment or onto electronic components. Visually inspect for signs of mechanical and electrical damage. Inspect for blown fuses and damaged relays. Inspect for loose or corroded connections, damaged wiring harnesses and/or switches. Check for a broken or partially broken wire inside insulation, which could cause system malfunction but prove good in a continuity/voltage check with system disconnected. Ensure any aftermarket electronic equipment is properly installed. If fault is found, repair as necessary. If problem still cannot be created, go to next step.
- Perform pre-check. See PRE-CHECK under SELF-DIAGNOSTIC SYSTEM. When pre-check confirms diagnostic system is functional, retrieve Diagnostic Trouble Codes (DTCs). See RETRIEVING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM.
- After problem has been identified and repaired, confirm repairs. See CONFIRMATION TEST under SELF-DIAGNOSTIC SYSTEM.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.