The HICAS system is Nissans' attempt at a super-handling 4 wheel steering type of thing, for anyone who's driven a car with 4 wheel steering in any sort of spirited driving, you realize pretty quickly that its less of an aid and more of a downfall.
|HICAS rear steering rack - 2 lines plug into it just behind the differential|
As the rear end steps out, the HICAS activates to counter the rear end slide, but because you expected the rear end to come out you've already begun to counter steer. So as you turn the wheel, the HICAS turns the rear wheels, and undoes what you've just done! Suddenly you're swerving wildly about battling the HICAS system for control of the rear end. It's a complete disaster and frankly a little dangerous. For even better control and handling look over this guide on Sway Bars, Understeer and Oversteer.
The solution is to yank it all out, the entire system, hoses, actuators, etc weighs approximately 60kg, so its a good way to shave some pounds off the already massive GTR. There are a few quick and simple solutions, that effectively lock out the HICAS but don't remove the weight, such as the Tomei kit which handles it electronically. There's also a number of kits that mechanically lock out the system by replacing the rear steering rack with a solid bar instead.
|HICAS Hydraulic Lines and Solenoid|
This guide is how to completely remove the system. You should have a bucket handy through-out because as you remove each part, power steering fluid (which is corrosive) will leak everywhere. To begin, remove the power steering pump by loosening the tensioner bolt from the under side, pull the belt off and rotate the pulley so you can remove the bolt through the hole in the pulley.Then remove the last bolt holding it in, on the rear and with the reservoir feed hose still connect, rotate the pump downward to gain access to the rear plate. Remove the bolts and lift off the rear plate, there are fins in the back side which drive the HICAS pumps, removing these fins will prevent the power steering pump from over heating once you've removed the HICAS completely.
|Removing the fins from the pump prevents the pump burning out|
Then you'll notice there is a power steering line that used to go from the solenoid to another line and this line is now not connected to anything. That line must be carefully bent and connected up to the other open line near the front.
This will create a loop for the power steering fluid, which still uses the cooler in the grill, so you cannot just block this line off. Once you've connected it in a loop, then the job is done. I know it's hard to see from just looking at the photos, but once you're in there getting your hands dirty it will be obvious which lines need to loop to where, just follow each line to and from the power steering pump and around the cooler. The photo below shows the lines looped together, you can see the grey line bent to shape and fitting in just under the black air piping.
|Nissan Skyline GTR Engine bay fuse box|
The last thing you'll need to do is head into the trunk, under the rear parcel shelf there is a control box for the HICAS on the drivers side, remove the 2 bolts securing it and look at the plug harness. Cut the green wire with the white stripe and tape both ends with electrical tape. This disables the HICAS ecu from reporting any problems. Altesrnatively you could also just remove the light bulb behind the cluster for the HICAS light but thats not as good as an idea because sometimes the HICAS lamp is used by the ECU in conjunction with other lamps to indicate other problems.