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.
Circuit Description
Ignition voltage is supplied directly to Fan Control (FC) relay coil. PCM controls the relay by grounding the control circuit through an internal switch called a driver. The primary function of the driver is to supply ground for the component being controlled. Each driver has a fault line which is monitored by the PCM. When PCM is commanding a component on, the voltage on the control circuit should be low (near zero). When PCM is commanding a component off, the voltage of the circuit should be high (near battery voltage). If the fault detection circuit senses a voltage other that what is expected, the fault line will change causing DTC to set.
The relay is used to control the high current flow to the A/C compressor clutch, allowing the PCM driver to only have to handle the relatively low current used by the 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.