there is a diagnostic test that involves stomping on the brake pedal quickly a certain number of times and simultaneously turning the steering wheel left/right quickly a number of times. i'm not joking.
i've seen it done on my GTR when the hicas (highly catastrophic a'hole system) was still installed and the sucker sat there stationary idling, twitching its wheels left, then right until the diag was switched off. there is a thread on here that describes the sequence, do a search and you'll prob fnd it.