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Old 04-20-2010   #1
jjskyline
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Default the rear steers a guide to HICAS

Ok so there’s always someone asking the question "what is HICAS?" "What does it do?" "Should I lock it out?” blar blar blar

Before I bought a Skyline I did a lot of research into this and found a whole load of information on it, but very little in definitive answers. A lot of the time things contradicted themselves or didn’t make sense, so…. I thought I’d write out what I now no about it. Also I found a lot of people quickly dismissed it as a waste of time.

One thing you will have to remember is the HICAS debate will rage on long in to the night and probably long after we have all departed from this world. Some will like it some will hate it.

I’m not saying I’m right by any means. All I want to do is try and give as much information over as possible relating to this subject that I believe to be true to the best of my knowledge.

So HICAS or SUPER HICAS is widely excepted too stand for High Capacity Actively Steers (Super HICAS was a updated version on later models)

Basically in a nut shell the back wheels are steered in the same or opposite direction according to several sensor feedbacks monitoring things like speed and steering wheel position.

There were two types, a hydraulic controlled unit or an electric controlled SUPER HICAS unit. They were found on several cars in the Nissan rage not just Skyline’s these included the 300zx TT and 240sx (se) optional extra) and some Silvia S13 models.

Many other Manufactures by the likes of BMW, Toyota, Renault and Subaru to name just a few that also adopted the Active 4 wheel steering or a variant of it.

Ok so how does it work?

The HICAS brain (the ECU found in the boot near the battery (R33 models) gets it information from sensors that monitor the steering angle, the speed the steering wheel is being turned and the cars speed. From this information the brain works out how much steering input to apply to the rear wheels. This then operates a solenoid valve that controls the flow of oil to the rear steering actuator. This is linked to the wheels a bit like a normal steering rack via a pair of track rods. The only difference is the amount of movement allowed. A maximum of 1 degree of lock can be applied at low speed and only 0.3 degrees at higher speeds. Find below a video of a 300zx in diagnostic mode showing you Maximum movement while stationary

YouTube- Nissan 300zx super HICAS
On the R32 GT-R’s with SUPER HICAS (some of the last ones made had it fitted) once the engine is on and the revs exceed 1500rpm the system is on. Then as the car is turned in too or out of a corner the rear wheels will steer the same way by an amount worked out by the HICAS computer (brain) from information and feed back from its sensors.

Having the rear wheels turning in the same direction has something to do with it “tracking” through the corner.

When the R33 GTR was introduced it was much more sophisticated. There were many more electronics to decided witch way to point the wheels and an electronic actuation to move them there

As well as a new rack one of the other things that was introduced was Yaw-rate feed back this helps with wheel deflection.

Now the Super HICAS system can monitor the drivers “intentions” for a corner. It does this by sensing how far and fast the steering wheel is turned, while calculating lateral G, actual yaw-rate and road wheel speed. This is then looked up against a table of pre programmed values that tells the computer (brain) how far to move the back wheels. This is continually monitored throughout the turn.

This real time info is compared against stored target values in the computers brain and the computer subtly realigns the wheels accordingly. All this happens in less then 1000th of a second or something stupidly fast.

The Super HICAS system was developed even further in the R34 GT-R when a Model Following Control System information loop was added this just increased the sensitivity over the previous version.

Now the interesting bit

The GT-Rs had a 4wd 4wheel steer integrated system. This was a very clever Advanced Total Traction Engineering System for All Terrains and Electronic Torque Split (ATTESA E-TS (pro) on the V spec) monitored several sensors at more then 100 times per second.

Basically on the straight and at first stage of steering the car is two wheel rear wheel drive. When the rears lose grip a hydraulic clutch engages and transfers power to the front wheels. It’s worked from feed back from the ABS, throttle position sensor and a lateral G sensor through a multi plate clutch not a viscous coupling. The stock Nissan set up ranged from 100% to 50/50 split

But What a lot of drivers fail to realize is that one of the parameters that governs this ATTESA E-TS is throttle position, meaning if you take your foot off the loud pedal the four wheel drive reverts to two wheel mode, so if you stick a GT-R in to a corner a bit too quick and bottle it half way through and lift off and reapply with an arm full of lock, your more then likely be facing the wrong way. 9 times out of 10 a HICAS failure is blamed.

Anyway that’s a bit off subject.

So your lights on the dash and/or its changing lanes

First off.

If there’s a light on, on the dash and no lock out kit is fitted 9 times out of 10 it’s a sensor fault of some kind. I am lead to believe that the rear wheels will “lock” dead straight as a safety precaution and HICAS is disengaged for one cycle. But codes are stored in ECU for 50 cycles. This would explain why many drivers feel an unsettled and not so planted rear end wobble. HICAS was designed to keep the car more planted at high speeds as well as help to corner and the Skylines that I have driven with a lock out bar do feel to me at least, “flappy” on the motorway

The other 1 percent of the time it could be low power steering fluid but this is found more on the Hydraulic controlled HICAS systems. In an R32.

The rear wheels will only ever move a max of 1 degree under normal conditions, anything more than that I would suspect worn bushes track rod ends and/or ball joints. A common failure and sometimes missed by even trained eyes. I have a Supra that liked to straight line wonder and that was down to worn bushes.

If you have up rated and /or lowered suspension: Make sure it’s been set up correctly. I would suggest a 4 wheel laser alignment to start and none, of that cheap Kwik Fit crap with a laser pen stuck on with blue tack on all 4 wheels. It appears that if your tracking is out it can also course the light to come on.

There is a HICAS reset that can be done. As there have been reports that Amps MPH Converter chips, Blue tooth and loud music can all interfere with the HICAS. I’ve been told that you disconnect the battery for 20 mins and pump the brake about 5 times.

I’m running a R33 GTST 1995 I’ve got a huge amp right under the HICAS unit running my 2x 400watt 10 inch Pioneer subs for the last 2 years. HICAS seems to be working fine light comes on for bulb test goes out and stays out. But that dose not mean yours will be the same.

The Steering wheel angel sensor sometimes comes off and needs to be put back on but the light on the dash will flash this code at you and your more then likely hear it ratterling around inside the wheel. Also if the incorrect steering wheel boss is not fitted with an aftermarket steering wheel your HICAS will not work correctly or at all.

So do you lock it out?

Well I think unless you have a R32 with hydraulic HICAS and its not broken or playing up id say no. (The first versions weren’t so clever) There is always the danger that it can fail at any time but so can any system from ABS to Coil packs from diffs to tyres some give you warning others just fail without.

I Can not believe that HICAS is as bad as many make out if it was used for so long by Nissan on so many models and then adopted and adapted and still used to this day by some manufactures it carnt be that bad with today’s stringent safety legislation.

If you decide to lock it out, on the R33 at least, it seems to be more controllable while in a “drift” and you can come on the power more quickly instead of hanging back for the wheels to straighten up. But why would I want to exceed grip and step the back out I’d want to maintain it unless you wanted to drift anyway? But then you would have locked your diff anyway right?

Anyway

Diagnostic mode can be entered by following if done correctly

Turn ignition off
Put in neutral
Turn ignition on and start engine
With in 10 seconds turn steering wheel from left to right, at least 20 degrees from neutral position
Then depress brake at least 5 times.

There are a few versions of this floating about but this one worked for me.

Then its just a case of looking up what the error codes (if any) that will be flashing at you on the dash. There should be a steady flash of .25 second intervals if all is ok

Hope this helps a few people.
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Old 04-21-2010   #2
DrMango
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Default Re: the rear steers a guide to HICAS

Very well put together writeup. Its much appreciated and Im sure it should help to curb some of the misunderstanding that surrounds the HICAS system

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Old 07-10-2011   #3
sb119
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Default Re: the rear steers a guide to HICAS

I know this is an old thread but awesome info! My GTR tends to wander when driving straight and I was contemplating removing the hicas but now I'll definitely have to look into worn out bushings..
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Old 08-22-2011   #4
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Default Re: the rear steers a guide to HICAS

with hicas removed can the 4wd stil work?
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Old 08-22-2011   #5
bobbo
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Default Re: the rear steers a guide to HICAS

Quote:
Originally Posted by BNR32 GTR View Post
with hicas removed can the 4wd stil work?
Yup!
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