Quote:
Originally Posted by crazyhorse
The FWD fuse under the hood forces the trans to open the transfer clutches. This "turns off" the AWD.
To get a bit more detailed, The transfer clutch(es) are controlled by the Transmission Control Unit (TCU). Using input from the ABS wheel sensors. The TCU varies how much slip the transfer clutch has, based on speed differences between the front & rear wheels.
When the fronts are on, say, ice, and you punch the gas, they start to spin. This sends a signal to the ABS unit, which forwards the signal to the TCU. The TCU then activates the duty "C" solenoid. This closes the clutch, sending power to the rear wheels.
Please note: I've skipped several details in making this easier for non-Soob geeks to understand. ALSO this does NOT apply to the 5MT.
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You're right, the TCU does vary the pressure it applies on the clutch based partly on the difference between the front and rear wheel speeds, but it does not determine this difference using the ABS sensors. It uses the speed sensors in the transmission. One measures the speed of the rear wheels and the other measures the fronts.
Also, the clutch does not 'close.' The solenoid you speak of 'flutters' open and closed at varying rates, which varies the amount of fluid going through the valve and therefore the amount of pressure applied to the clutch.