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Discussion Starter #1 (Edited)
Hi all, as we all know there is absolutely sod all information available about these cars on the net, which is a real surprise given their status and popularity. One of the main things people constantly have issues with is the HICAS, so I thought I'd try making a fully comprehensive guide as to how the HICAS works, what parts the system consists of, where all these parts actually are including any relays, which way the wiring finds it's way though the car, etc. With pictures if possible. I also intend to make a full guide of how to fix it when things go wrong. I also could do with knowing what's done about the electronics side of things when people fit a HICAS lock out kit. I don't know it all, so I need as much help and feedback from you guys as possible in order to do this, along with pictures so it's easy for people to identify what's what in future. Hopefully we'll all be able to figure it out together and then have a solid resource for the future.

Anyway, here's what I know (or have dug up from various parts of the net) so far to start us off:

What is HICAS?

For those who don't know what it is, HICAS is basically the system that oversees steering for all four wheels, and stands for High Capacity Actively Controlled Steering. Earlier Nissans like the R32 used a hydraulic system which had speed sensors and used the power steering pump to steer the rear wheels. The HICAS ecu controls the two valves at the front and rear of the car, which control the amount of fluid that passes through the rear rack resulting in the amount the wheels turn when cornering. Slower you corner the more they steer, the faster you go the less they steer.

Other Japanese manufacturers offer four-wheel steering and in the case of Honda and Mazda it is two-phase, assisting low-speed manoeuvres as well as enhancing high-speed stability. HICAS is also two-phase, but it is not arranged to make it easier to squeeze into parking spaces. The rear-wheel steering, which never exceeds plus or minus 1 degree, is purely designed to improve the cars response in medium and high-speed swerves.

The rear-wheel steering system, which is integrated with the suspension and the front-wheel steering, is electro-hydraulic. It operates like this: electronic sensors detect the cars speed, steering angle and steering wheel movement, and if they exceed predetermined values, the computer directs a hydraulic actuator at the rear axle to steer the rear wheels via the rearmost lower suspension links. In normal driving the movement is rarely more than 0.4 degree.

But, unlike other 4WS systems which, at speed, steer the rear wheels in the same sense as the front ones, HICAS first introduces a twitch of counter-steer before settling with all four wheels pointing in the same direction. The degree or suddenness of this touch of opposite lock is reduced as the speed rises.

HICAS automatically produces a precise form of the rally drivers technique of flicking the steering to the outside of the corner before turning into it. The result for the car is very sharp turn-in, with better stability through the classic lane-change manoeuvre which reproduces emergency evasive action at speed. An ordinary car tends to swing its tail in such circumstances, but this system allows the front and rear tyres to develop their slip angles simultaneously to the benefit of handling.

What's the difference between HICAS and super HICAS?

The newer version of this system is called Super HICAS, and was used from the R33 onward. Super HICAS is different from earlier versions as the rear wheels are now steered electronically by a motor mounted behind the rear differential, and an onboard control unit adjusts the rear toe angle by a degree when the system sees fit. This version saved weight, and is said to be a much improved system. The Super HICAS system also oversees the power steering on the front of the car, varying the assistance depending on vehicle speed, and monitoring what you're doing with the front wheels to decide when to alter the rear toe. As you can see in the illustration below, the steering assistance decreases the faster the vehicle is travelling:



More on the failsafe area of the illustration in the next section.

Should I remove the HICAS?

These HICAS systems help improve cornering stability and give the car a more nimble feel, and it does it's job well if it's working correctly, making the car more stable for the average driver. On a racetrack however, it's been said the HICAS can become too intrusive and unpredictable, particularly on long high-speed corners, counter-steering is often needed to correct the Skyline though the corner, and this is not good for lap times. A lot of owners fit a lock out bar to disable the HICAS system which people claim can improve the car's balance, resulting in more predicable handling and faster lap times on track. Fitting a HICAS lock out bar (as the name suggests) locks the rear steering mechanism so it can't move - for a number of reasons: letting you remove all the HICAS gubbins for weight reduction; drifting and whatnot. All of these are fair enough, but another main reason is people just not being arsed to fix the system properly when it gets wobbly, so resort to ripping it out. Another point has been raised in the past, that if test drivers think it doesn't give "real benefit" until 120mph+, why did Nissan fit it to their japanese cars which were restricted to 112mph? Anyway, here is another couple of diagrams, showing how these HICAS systems can improve stability during high speed manoeuvres:




If this mechanical trickery doesn't do it for you and you decide you want rid, there are a few options. You can fit a lock out bar, which replaces the rear steering rack and motor assembly, fixing the rear wheels. You then have to leave the HICAS ecu in place to control your power steering, and remove the HICAS bulb from the instrument cluster. The downside to this method is the HICAS ecu can revert to "failsafe mode" since it sees some of the system is now missing. This prompts the HICAS ecu to fix the power steering assistance at a set rate (as shown in the illustration above), the amount of assistance it'd give if the car was travelling at near enough 110mph. So basically as little as possible without the rack going stupidly hard. This is why the majority of people report their power steering gets heavier when removing the HICAS. When fitting only a lockout bar, DON'T remove the HICAS ecu, as then there would be no power steering at all! Here's a picture of a lock out bar fitted:


Another way of fixing the rear wheels is to fit a Tomei HICAS eliminator kit. What this comprises of is a little electronic box that you wire into the HICAS ecu wiring loom, which tricks the HICAS ecu into thinking all is well. You also have to shim the HICAS rack to prevent movement. This method will not make the HICAS warning light illuminate, and still give you the full speed variable power steering since the HICAS ecu doesn't see anything wrong. Here's a picture of the kit, and I'll include fitting instructions if I find any:


The final way, and in my opinion, the best way, is to fully remove the setup if you don't want it. Do do this you need an s14 rear subframe, rear control arms, some s14 bushes to go in place of the HICAS balljoints in the rear knuckles, and importantly an s14 front steering rack. With the s14 rack, it doesn't depend on the HICAS ecu to control the power steering, so now you're safe to remove everything related to the HICAS, including the control unit and all HICAS wiring if you're wanting to do a little weight saving.

If you have an r32, you have HICAS instead of Super HICAS, and is a little different to remove. Here's a link to show how to remove it on an r32, and still keeping the speed sensitive power steering:
http://forums.gtrcanada.com/gts-tech/9067-how-r32-gts-hicas-removal.html

HICAS components and their locations:

Here's an illustration showing the components of the HICAS system found on the R32 and other similar aged Nissans:


The remainder of this section is based on the Super HICAS setup fitted to an R33, as that's the car I own so that's the pictures I can get. The locations are similar for all Skylines though.

The main brain of the Super HICAS system in an R33 is located near the battery in the boot, hanging from underneath the parcel shelf. Note they are different internally depending on the age of the car, early units have two circuitboards inside, whereas from July 1995 the unit has just one board. They're interchangeable, and the change appears to just be a way of reducing manufacturing cost per unit. I've tried both versions on my spec 1 and can confirm they both interpret the vehicle speed the same according to consult, and the only difference in operation I've spotted so far is the way the HICAS light separates error codes differently in diagnostic mode. The mounting brackets on the unit can be different depending on if your car had ABS or not, but if you need to change brackets over, the whole cover just unscrews from the unit and can be swapped over to suit.

This is what the ABS fitment HICAS unit looks like:


And this one is for a car with no ABS:


If you're interested in the differences inside the two control units, here's a picture to compare:


Here's another picture showing where the HICAS unit normally hides away. On non ABS cars it's hanging from the parcel shelf on it's own, but if like me you have ABS it's the larger unit of the two, closest to the parcel shelf above the ABS unit:


This is the HICAS motor which the system controls to adjust rear toe, and is to the rear of the rear diff:


This is the rear steering rack, which the HICAS motor is attached to:


This is the steering angle sensor, fitted onto the steering column, and is rotated by the steering wheel:


This is the location of the HICAS relay on the R33, the blue lump just next to the boot lock:


This is an electrical valve that's fitted to the front steering rack, and is how the HICAS alters the assistance of the power steering based on vehicle speed:


Diagnosing HICAS problems

If you're having problems with the operation of the HICAS system, it has a diagnostic mode you can attempt to run. Note that bizarrely this diagnostic mode won't work if there is still a current issue with the system, which is an absolute stroke of genius! In this case, you CAN still check the HICAS system with Consult provided you have the software to do so. Anyway, when you start the car (provided the HICAS light is off), if you rapidly rotate the steering wheel a few times and then press the brake pedal five times in quick succession, the HICAS light starts displaying error codes, with long flashes indicating tens, short flashes indicating ones.

The R32 error codes are as follows:

1 - HICAS solenoid right hand
2 - HICAS solenoid left hand
3 - Cut off valve
4 - Power steering solenoid
5 - Vehicle speed sensor
6 - Steering angle sensor
7 - Neutral position sensor
8 - (Auto) Parking brake sensor, (Manual) Clutch sensor
9 - (Auto) Inhibitor switch, (Manual) Neutral sensor

The R33 and R34 error codes are as follows:

11 - HICAS control unit
12 - HICAS motor power supply not present
13 - HICAS motor output not present
21 - vehicle speed sensor not present
22 - steering angle sensor not present
23 - steering angle sensor neutral or not present
24 - rear main sensor input not present
25 - rear sub sensor input not present
31 - parking brake sensor input not present
32 - (auto) inhibitor switch input not present, (manual) neutral switch input not present
33 - engine speed signal not present

Before repeating the error codes, the HICAS light flashes quickly ten times so signify the end of the stored error codes if you have the older control unit, or just one long flash if you have the newer unit. Once you've done this, you can enter full diagnostic mode by driving forward a few feet. This then prompts the HICAS system to run a self check, twitching the rear wheels every couple of seconds to make sure it can move them. You can also test the rear steering yourself by turning the steering wheel, you should see the rear wheels turn in time with you rotating the steering wheel. After 5 minutes, driven over 25kmh (or mph depending on how your speedo has been converted), or turned the car off, the HICAS diagnostic mode will then shut off and should return to normal.

Here's a video I found on youtube demonstrating how to start the HICAS diagnostic mode:

HICAS diagnostic mode

If you REALLY have to start checking the HICAS system over, checking voltages, referring to flow charts, etc, here is an online version of the 300ZX power steering and HICAS workshop manual, which covers the hydraulic system similar to the R32. From 94 onwards I think, the Z32 then uses the later electronic version which is near enough identical to the R33 and R34 setup apart from wiring loom differences and part locations. The information for the speed sensitive power steering stuff is from page 29 to 42, with the HICAS specific stuff from page 43 onwards:

Power steering and HICAS workshop manual

If you need to see wiring diagrams, perhaps looking at these images would prove easier than trying to find them in the link above:

R33 Super HICAS wiring diagram
R34 Super HICAS wiring diagram

Common problems that affect the HICAS

Aside from worn balljoints which are expensive to replace, the two most common issues when overlooked that affect the operation of the HICAS system is the speedo conversion method and the fitment of aftermarket steering wheels. You need to make sure your aftermarket wheel is using a HICAS compatible boss so it can rotate the steering angle sensor, and a lot of speedo converter chips can also cause problems. The best way around this is to actually recalibrate your speedo instead of using converter chips. I personally feel it's important that the HICAS system knows the correct speed the car is travelling at all times since the power steering and and rear toe adjustments all depend on the vehicle speed. There are numerous ways to convert the speedo to read in MPH, but most of these methods trick the engine ecu and HICAS control unit into thinking you're going slower than you truly are to a certain extent, and some methods are worse for this than others. Like I say, this doesn't just affect the rear steering, but also the power steering on the front as this is also speed sensitive. If you want the various control units to know the correct speeds at all times, here's my guide to converting the speedo 100% accurately:

The way Nissan convert the speedo to MPH

That's it so far, but please feel free to contribute, and if I find anything else out I'll keep adding as I go.
 

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Stu I think is a good idea mate
TBH though most dump the hicas with the lock out bars or Bicas or similar,
Personally I didn't like it as we had an evo before and sierra's so it felt fidgety all the time, especially after it nearly killed me .. twice lol
But I'm sure though your guide will be a helpful option to those who don't want to lose it :)
Matt
 

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Discussion Starter #3 (Edited)
Even elaborating on how you'd normally remove the HICAS would help me fella. Such as what happens with the electronic side of things once the HICAS rack has been removed. Is the control unit left in place to still control the power steering, or do you know of a workaround so you don't need it? Or do you just take the HICAS bulb out?

Literally anything to do with the system, component locations, or even removing the setup will be of help. If removing, how much of it do you remove, what happens with the power steering afterwards and why, etc.

At the moment, the only answer people get when discussing HICAS faults is to remove it. I'd personally prefer to understand the system instead of just junking it, hence this thread.

At the very least it might help me find out why the power steering goes heavy when removing the HICAS, so could still be of benefit to everyone on here whether they've kept the whole setup or not.

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I found out that the HICAS ecu between a spec 1 and 2 are diferent yesterday. Spec 1 is a 2 level circuit board where as the spec 2 is one level. Must of had a rethink between the two. Not sure if that's helpful or not lol
 

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Good idea stu if you download the R34 manaul theres a fault finding guide in there on hicas which is pretty similar to the r33 and has some handy information plus i had some other PDF with good information pm your email ill send them over if want.
 

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Worth mentioning, cheers. Did it still work, or is it not compatible like I'd suspect? I'll add it to my main post above.

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It works fine main. Straight swap. Only difference is the mounting bracket in the boot
 

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I don't no sorry. I'm going to fit a lock out bar anyway only bought it to get my steering working properly again.
 

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Discussion Starter #13 (Edited)
What's your power steering like? Does it get heavier if you unplg the HICAS unit, or is it permanently heavy now anyway? I wouldn't have thought the steering angle sensor would matter any more as that's just for the HICAS ecu to determine when to turn the rear wheels, so I figured you'd be okay without a HICAS boss in your case.

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not driven mine as of yet, but ive fitted a full hicas eliminator kit, removed bulbs in clocks and left ecu in place. i shall keep you posted how the steering feels :D
 

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Just like to add, if you are looking at disabling the hicas, tomei hicas eliminator kit is really good. No striping off the steering rack just fit 2 shim's on it, connect 3 wires on to the hicas ecu and that's it all done. Saves taking out the dash too just for 1 little bulb. No heavy steering all is good. Pukka bit of kit if u don't wanna remove it all.
 
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