It's a common thing to do, there should be some info on the web about it. I haven't done it though, still using HICAS. There are two versions, the early ones being hydraulic and the latter being electric actuated via a motor. Perhaps if you have the electric version, pull the fuse to disable it. If Hydraulic, perhaps do the same thing and fit the rear locking bar at the back. After all the years, the rack ends develop free play which affects the operation of the rear steering. The rack ends are easy to replace though if wanting to keep HICAS. The HICAS cylinder itself rarely fails but people have experienced some crazy mishaps for some reason. I'd say most likely to do with the electric side of it.
