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.
ECM Power Source Circuit: Description
When the engine switch is turned on (IG), the battery voltage is applied to terminal IGSW of the ECM. The ECM MREL output signal causes a current to flow to the coil, closing the contacts of the EFI MAIN relay and supplying power to terminal +B of the ECM.
If the engine switch is turned off, the ECM holds the EFI MAIN relay ON for a maximum of 2 seconds to allow for the initial setting of the throttle valve.
When the engine switch is turned on (IG), voltage from the ECM's MREL terminal applies to the integration relay (EFI MAIN relay). This causes the contacts of the integration relay (EFI MAIN relay) to close, which supplies power to terminal +B or +B1 of the ECM.
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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.
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