Hall sensor is in the Dizzy and the BCM is the Body control Module, it also include the smartlock. It is located in the dash approxomatly where you left knee would be when sitting in the drivers seat.

Hall effect device is in the dizzy where points normally are.

And yes - headsmack - the BCM playing up can do this sort of thing too - it's mounted behind the dash panel on left side of the steering column - above driver's left knee / leg.