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.
Fan Control
The PCM monitors certain parameters (such as engine coolant temperature, vehicle speed, A/C on/off status, A/C pressure, etc.) to determine engine cooling fan needs.
For Variable Speed Electric Fan(s): The PCM controls the fan speed and operation using a duty cycle output on the Fan Control - Variable (FCV) circuit. The fan controller (located at or integral to the engine cooling fan assembly) receives the FCV command and operates the cooling fan at the speed requested (by varying the power applied to the fan motor). See Fig 1.
For Relay Controlled Fans: The PCM controls the fan operation through the Fan Control (FC) (single speed fan applications), Low Fan Control (LFC), Medium Fan Control (MFC) and/or High Fan Control (HFC) outputs. For three speed fans, although the PCM output circuits are called low, medium and high fan control (FC), cooling fan speed is controlled by a combination of these outputs. See Fig 2.
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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.