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.
Control Unit
The Electronic Control Unit (ECU) microprocessor receives input signals from various sensors, switches and ignition and starting system components. The ECU uses this information for controlling various functions. See OUTPUT SIGNALS .
The ECU has constant battery voltage at BATT terminal. The EFI main relay provides battery voltage to terminals +B and +B1 of ECU. The EFI main relay is activated when ignition is turned on.
The ECU contains a fail-safe function, used in case of sensor or switch failure. The fail-safe function uses preprogrammed values to provide a limp-in mode for minimal driveability or may shut off engine.
The ECU is equipped with a self-diagnostic function. Trouble codes are set by the malfunction of various engine sensors, switches or circuits and stored in the ECU memory. When trouble code is stored, the CHECK ENGINE light on the instrument panel will come on.
| Model | Location |
|---|---|
| Camry | Behind Glove Box |
| Celica, Corolla, Paseo & Tercel | Bottom Center Of Dash, In Front Of Console |
| Cressida, Land Cruiser & Supra | Above Glove Box |
| MR2 | Left Rear Of Engine Compartment |
| Pickup & 4Runner | Behind Passenger-Side Kick Panel |
| Previa | Under Driver's Seat |
NO RELATED
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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.