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.
Chart C12 - Cooling Fan Control Circuit (5.0/5.7L) (2 Of 2)
The cooling fan is totally controlled by the ECM based on inputs from the coolant sensor and fan control switch. The fan should run if coolant temperature is more than 221°F (105°C). Battery voltage is supplied to the fan relay on terminal "E" and ignition voltage to terminal "C".
Grounding circuit No. 335 (relay terminal "B") will energize the relay and supply battery voltage to the fan motor. Once the fan relay is energized by the ECM, it will remain on for a minimum of 5 seconds. The ECM will remove the ground to circuit No. 335 if vehicle speed is over 40 MPH unless the engine is overheating.
The fan control switch is mounted in the A/C high pressure line and will open when head pressure exceeds 233 psi (16 kg/cm2 ). This input causes the ECM to ground circuit No. 335. On a vehicle without A/C, circuit No. 732 is connected to ground to prevent the cooling fan from operating at all times. If Codes 14 or 15 sets or the ECM is operating in the fuel back-up mode the ECM will turn on the cooling fan. For code testing procedures, refer to the V6/V8 PFI TESTS/CODES article in this section.
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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.