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.
Diagnostic Procedure (RX300)
2004 Toyota Celica GT, StandardSECTION Diagnostic Procedure (RX300)
WARNING: This page is about a different car, the 2003 Lexus RX 300 and 2003 Lexus ES 300. However, it is still accessible from the selected car via links, so may be relevant.
- Access ECM behind glove box. Turn ignition on. Backprobing connector, connect DVOM negative lead to terminal No. 17 (Brown wire) at ECM E8 connector and positive lead to terminal No. 16 (Black/Red wire) at ECM E5 connector. See Fig 1. If 9-14 volts is present, ECM power circuit is okay. Diagnose by symptom. See SYMPTOMS in TROUBLE SHOOTING - NO CODES article. If 9-14 volts is not present, go to next step.
- Check for an open circuit in Brown wire between ground and terminal 17 at ECM E8 connector. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Repair as necessary. If wiring is okay, go to next step.
- Measure voltage between chassis ground and terminal No. 2 (Black/Orange wire) at ECM E5 connector. If 9-14 volts is present, go to step 5. If 9-14 volts is not present, check IGN fuse in instrument panel junction box under left side of instrument panel.
- If fuse is blown, repair cause of blown fuse. If fuse is okay, check ignition switch. See appropriate STEERING COLUMN SWITCHES article in ACCESSORIES & EQUIPMENT. Replace ignition switch as necessary and retest. If ignition switch is okay, repair open circuit between battery and ignition switch, or between ignition switch and ECM.
- Turn ignition on. Measure voltage between chassis ground and terminal No. 8 (Black/White wire) at ECM E5 connector. If 9-14 volts is not present, replace ECM. If 9-14 volts is present, check EFI fuse located in engine compartment fuse/relay box at left front of engine compartment. If fuse is okay, go to next step. If EFI fuse is blown, repair cause of blown fuse.
- Check EFI main relay located in engine compartment fuse/relay box at left front of engine compartment. See RELAYS under RELAYS & SOLENOIDS. If EFI main relay is okay, check circuit between chassis ground and terminal No. 8 at ECM E5 connector. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Repair as necessary. If circuit is okay, repair circuit between battery and EFI fuse.
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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.