I hadnt looked at mine yet, but is this a aftermarket electric fan or pulley mount fan? Pulley mount fans are notorious for having the fan clutch going bad. You can buy new fan clutches at any parts store and replace yourself.
I hav never come across a sensor that would cause the fan to stay engaged. The fan clutch is nothing more than a coiled spring and sealed bearing. As with age and excessive heat, the spring fails to contract and tighten up. Thus causing it to stay locked up. I hate to say it, but almost guarantee your are in for a 2 hour repair.
It's not your ordinary fan. It's a visctronic type fan (VDF) that runs at varying duty cycles based on an input from the PCM. There's also a sensor that provides speed feedback to the PCM. The PCM uses inputs like ECT, EOT, transmission temp, intake air temp, A/C load, etc.... to determine the duty cycle.
A bad sensor, erroneous input to the PCM, or short to ground on the actuator power circuit among other things can affect how the fan operates.
Does the fan run all the time with the A/C and defrost both off?
What do you mean by "the fan is on"? The fan will always turn. Mine is an 03 and my fan has only come on a handfull of times and every time it does it scares the HELL out of me. You know when they come on!!!
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