I have got confused now - as to which thread is for the switch mech!
But as I found this thread first - here we go - a bit more techy info fur ya to peruse......
The Driveline
The X-Trail uses an electronic four-wheel drive system that owes more than just a hint of its design to the original ground-breaking Skyline GT-R system. Like the GT-R, it uses a wet multi-plate clutch to vary the torque split between the front and rear wheels, however, in the Skyline, the driveline was predominantly rear-wheel drive with torque directed frontwards only as necessary. In the X-Trail the opposite applies - the car is predominantly front-wheel drive, with torque directed rearwards as required.
diagram shows the layout. A transfer case turns the drive through 90 degrees, sending it along a propeller shaft to the rear diff. In the extended nose of this differential assembly is a wet multiplate clutch ('coupling') that apportions torque to the rear wheels. With the coupling unlocked, no torque turns the rear wheels - the car is pure front-wheel drive. With the coupling fully locked, the front/rear drive is 57:43, a ratio determined by the transfer case. Thus the greatest amount of torque that can be directed through the rear wheels is 43 per cent.
The electronic control system uses inputs from the accelerator opening (not throttle opening - that doesn't vary in its opening angle linearly with the accelerator, remember!) and engine speed. Additionally, an accelerometer (g-sensor) inputs its signal into the control unit. It's not completely clear from Nissan literature, but we assume that the g-sensor measures longitudinal acceleration, as its input is also used by the ABS part of the system.
I still have no details of the Frontera system, but am still looking - if anyone else can help - please do.