4WS Overview
Contents
Overview
(Please note for any location info this is based on a 91 jdm convertible- some locations for coupes will be slightly different)
The 4ws system was only available on JDM celicas (other manufacturers had similar systems but not the same eg Honda etc) therefore there is no English workshop manual. If you can read Japanese then make yourself known!
Whilst the Jap manual is readily available the only sense to be made is using the pictures which, actually, do give quite a good indication of some diagnostic checks and wiring diagrams.
The idea of 4WS is to, at slow speeds below 30kph (ish) where the wheels turn opposite the front wheels, is to give a tight turning circle to aid manoeuvrability, which it does! Black cabs aren’t the only ones that can do that tight turning you know!!
At speeds over around 30kph the wheels turn in unison so say you are on a motorway the car will ‘crab’ across lanes rather than turn. When going fast it is supposed to negate oversteer and give a lot of grip through the corners.
There are 2 buttons on the dash for the 4ws system. 1 is rev2ws which forces the back wheels to centralise but ONLY in reverse as apparently some people struggle if the back wheels are not fixed when going backwards….. I think it makes it easier TBH. The other button is a sport/norm switch. Not too sure what this does but am told it makes you go round corners like on rails, even more so than if you had the switch in normal mode?
There are 7 main bits of the 4ws system : 1) The main 4ws ecu – mounted nsr wing in boot 2) The steering driver 4ws ecu – mounted next to the main 4ws ecuin boot 3) The speed sensor (or it uses abs system if equipped) – nsf hub held on by 10mm bolt and rust 4) The steering controller switch – mounted to 4ws rack n/s 5) 2 relays in engine bay , n/s against wing in middle (1 for main motor, 1 for backup motor) 6) Main motor – n/s of rack 7) Backup motor (why this is called backup I have no idea, more of a secondary as it uses both motors) – o/s of rack
4WS problems
These are some of the problems I have had or I have heard of.
1) 4ws light on and back wheels don’t turn at all – not so common 2) 4ws works at standstill but light comes on when moving off (usually when turning)- not that common 3) Wheels turn in same direction all the time making slow corners very unpleasant- vvvvvv common 4) Wheels turn in opposing direction all the time causing you to fall off the road into a bush – rare
The failsafe seems to be number 3. I assume so that if you are steaming along it wont upset your driving too much. Where as if it reverted to number 4 then you may ditch it.....
The 2 main components that fail appear to be the speed sensor and the backup motor.
The speed sensor which (on non abs cars) is located on the n/s/f hub and is basically just an abs type sensor. These break for fun and cause problem 3) & 4). If the sensor can’t tell what speed your going then your wheels are going to do what they like! If you get code 41 then chances are your sensor has bust.
If this sensor does fail then it is a NIGHTMARE to replace. They usually ( unless put in with copper grease etc) seize in and when pulled the back snaps off so the wire part is in your hand and the main sensor part is stuck in the hub. Either get another hub or drill down the centre of the sensor in the hub (no more than 14mm or you’ll hit the inner hub and that would be bad….) and try and extract it bit by bit. (by drilling the hole in the centre is lets pressure off the outer rim). Try to avoid chipping bits off as you don’t want them flying around the hub!
The replacement sensor is around £120 from Mr T.
Do not lose hope just yet though as I have come across some info on my travels that says an abs sensor for a 1992 Toyota Camry is almost the same part. It does require slight modification (to the retaining brackets and you will need to use the wiring plug off your duff sensor) but these can be had for around £40-£60 off ebay and suchlike. The part is made by a few places – Raybestos ABS530165 and Standard ALS267. You may need to get them sent from America but it will still be cheaper. If you’re not into modifying parts to suit then go for the original, at least it will fit. REMEMBER COPPER GREASE!!!!!!!!!!!!!!! The sensor will still break after a while but at least it will be easy to change.
The other swine for conking out is the backup motor. The backup motor is the smaller of the 2. As you stand at the back of the car and look forward it is the one on the right (it also has flatish sides compared to the cylindrical main motor). They look very similar to windscreen wiper motors but are smaller. I thought they’d be massive but they are very small.
To get at said motors you’ll need to get under the car at the back (I didn’t need to jack mine up at all and I’m a big boy…..) and look towards the rear axle area. You will see a metal cover plate in the centre of the axle. This is held on by 4 12mm (head size) bolts. Mine were easy to come out but has lived in Japland most of its life so may be worth a good dousing in plusgas, rostoff (made by wurth, the best freeing off spray i’ve ever come across) etc. Also I had to remove 2 10mm bolts holding the wiring channel to the cover plate. The plate should now be free and you should be faced with the 2 motors sticking out either side of the rear rack. You will need to remove the wiring channel as well if you’re removing the motors. That’s just a couple more bolts and some nasty clips to free the wiring from the channel.
To remove the motors
I found it easier to remove the entire motor assembly as space is limited and it helps as you can then test the rack for stiffness/being jammed whilst you’re at it.
You need to unplug the 2 motor connectors. On the cabby they are in the boot. Behind the carpet on the back bit where the back lights attach, in the middle, you will find the connectors. These come into the car from the boot floor at the back and to the left of the spare wheel well along with the steering controller wire (that leads to a sensor attached to the rack)– leave this for now. You’ll need to get the grommet out of the boot floor as well . One connector was blue and the other white.
The motor hub is held on by 4 bolts/screws. The top 2 are got by using a 10mm socket and extension above the motor hub and whipping them out. The 2 bottom ones are on the back of the hub as in facing the front of the car. DO NOT use a screwdriver to undo these as if you mangle the head you will have to drop the entire rack to get to them to extract them. The assembly isn’t heavy but it will fall on your head so support it whilst undoing the bolts!
When that’s off you can then check the rack isn’t jammed. Look at the end of the motor hub you’ve just removed and you’ll see a square drive. You need to find something similar, to enable you to turn the rack (the bit still attached to the car). I used a large flat blade screwdriver. Just turn it back and forth end to end (about 30 turns). Nothing will actually happen (the wheels wont move) but it has been known for the rack to jam at its furthest travel and this can free it. If it’s really stiff then you have major probs and will have to take the rack out to investigate/ grease.
Back to the motors. Leave them attached to the hub for now. To test them get yourself a battery (12v) and power the motor up directly from the battery. Doesn’t matter which terminals you use as you need to test it in both forward and reverse. Do same for both motors.
You can fuse the wires you’re using if you want in case of a short. The motors should just spin the square drive of the hub smoothly forward and back. The main motor is a bit faster than the backup. If the motor just hums and does nothing chances are your wires will start getting hot or your fuse will go pop so be careful.
If either motor doesn’t work as it should then you’ll need to strip it and see whats going on. If you don’t know how to strip motors then DON’T DO IT! These babies are rare enough without you destroying them. There is loads of info on the web on how to test, strip, repair motors but any electrical engineering place should be able to sort them. Common motor issues are seized shaft, worn brushes, knackered windings.
If you do decide to take the motor cover off to have a butchers you will need to undo 2 screws. At the bottom of the motor you will see 4 screws (or what were!). These rust soooo much. 2 hold the motor cover on and 2 hold the motor to the hub.
Mine were totally un-undoable so I had to dremel the heads off.....If you pull the cover off do it slowly as attached to the inside of the cover are the motors magnets. /these will pull the main shaft out of the hub and knock the brushes out of place- /they are an absolute nightmare to put back – you have been warned........
Note that these motors are unique to Toyota 4ws systems and you wont get them anywhere else. The hub unit with the 2 motors is still available from Mr T but will set you back around $2000. Yes you read that right.
So thats the motors which takes care of codes 21,22,23,24,31,32. (there could also be other faults associated with these codes however but from the motors point of view this is it).
The steering control sensor
This tells the system where the back wheels are. It is just a potentiometer so at one end it will have a reading of so many ohms and at the other a larger reading. To remove this sensor you just take out the 2 screws and it pulls out. If you replace this sensor or disturb it then it will need re-centring. To adjust it merely loosen the bolts and twist to gain the required reading on your ohmmeter as follows..........
.Make sure the rear rack is centred. There is a bolt hole below and to the left of the square drive where the motors fit. When the rack is centred you will be able to screw a bolt in which will show the rack is centred. (remember to remove the bolt!)
Disconnect the wiring plug and look at the terminals on the plug in your hand. You’ll see 3 prongs. The 1 on the left we’ll call pin 1, centre is pin 2, right 1 is pin 3. Get your ohmmeter and measure between 1 & 3. Divide this reading by 2 and then add 0.1 ohm. Remember this number. Plug the sensor back in and measure between 2 & 3. This should match the figure you have just remembered. If it doesn’t you’ll need to adjust then sensor position by twisting it and trying again. Trial and error i’m afraid.
The 2 relays for the motors
These are located in the engine bay on the nearside halfway along the wing. They are identical. These don’t appear to go wrong. I have not heard of an instance when they have gone wrong. They are 4 pin relays which can be tested. Have a look on the web for testing relays, it’s not hard.
The 2 ecu’s
On the cabriolet they are on the n/s/r wing behind the carpet. They are attached to a metal plate which you have to remove in order to get to the ecus. If one of these goes I presume replacement is the only option but try recentring the steering control sensor before resorting to a new ecu. I believe the coupe versions are located in a similar location.
Wiring
There is masses of wiring relating to the 4ws system. If you have a fault that just can’t be sorted through motors, sensors etc then you may well have a wiring fault in which case you have no option but to trace every wire or obtain another loom (i’m sure thats not easy though). Obviously you can disable the system completely by locking the rack up or replacing the back end with non 4ws components.
Apparantly someone has had success disabling the system by centralising the rack and disconnecting both motors. How this worked i do not know as the shaft is still attached to the front rack. Apparantly it worked though...................try this at your own risk.
One point I came across which seems to be quite well known but wrong is that if you’re rear wheels don’t centralise when the rev2ws button is pressed and reverse is selected then your backup motor is duff – This is not the case as my own car had a duff backup motor but did centralise.
THE END! For now
Please note this is all based on my own experiences, hours, days, months of searching the web for other peoples experiences. It is still worth searching as there is more info out there to be found. I shall update as and when I find something out.
Rammers
