had that issue with mine. Do you have an aftermarket steering wheel fitted? or the stock nissan item. because i've heard the stock one has steering angle sensors.
the r33 hicas steering rack is electronic, so could be something to do with it.. i had an aftermarket steerer, and the hicas light was always on, and steering was heavy.. on random occations the light would turn off and steering would be light again..
hicas is over rated anyway