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.
MFI Relay
MFI relay switches power to vehicle sensors and actuators including Volume Airflow (VAF) sensor, Crankshaft Position (CKP) sensor, Camshaft Position (CMP) sensor, Idle Air Control (IAC) motor and injectors. Relay failure will cause a no-start condition.
- Remove MFI relay. Check resistance between relay terminals No. 2 and 4. See Figure. Resistance should be about 70 ohms.
- Connect jumper wire between battery positive terminal and relay terminal No. 4. Connect second jumper wire between battery negative terminal and MFI relay terminal No. 2.
- With relay energized, continuity should exist between terminals No. 1 and 3. With power source removed, continuity should not exist between terminals No. 1 and 3. If relay does not test as specified, replace MFI relay.
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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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