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.
Flexible Fuel (FF) Sensor
FF sensor is a capacitive device with a signal processing stage. FF sensor is located in engine compartment, high-pressure fuel supply line between fuel mixer and fuel rail. FF sensor frequency signal varies according to conductivity and temperature of methanol-gasoline mixture. As percentage of methanol in fuel increases, output frequency of FF sensor signal will increase. For example, a fuel mixture that was determined to be 30 percent methanol will result in FF sensor signal output frequency being 60-100 Hz. Sixty percent methanol will result in FF sensor signal of 90-130 Hz. The PCM uses FF sensor frequency signal to calculate correct air/fuel ratio and spark advance.
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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.