4WS Troubleshooting - Gurus please!

[NakiCurren]

Hi,

I see there have been a few threads on this earlier, but almost all on early models, and none that have solved my problem yet!

I have a '94 ST207 (4WS Curren) with 183k on the clock and I have a fault in my 4WS system somewhere..

It started out as a very intermittent 'glitch' where it would trip out, and turn the rear wheels in the wrong direction. Easily solved by turning the car off, and re-starting (sounds like something from Microsoft - only I didn't have to close any of my open windows ) Then all was good for 4-5 months until it started to trip and stay tripped for a couple of days, and then mysteriously come right again. These symptoms lead me to think that this may be due to a broken/faulty connection somewhere?

Now it's permanently in fault. Toyota dealer plugged their diagnostic machine in, and prescribed a new 'Steering Converter' ($2k ex Japan, or $300 for a secondhand one), before charging me horribly!

Needless to say, I'd rather not blow that sort of dosh on something that may not even be the cure!

Looking through the forums here, it seems that it could be one of three things:
1) Speed sensor in the front left hub is dodgy.
2) Electric motor, or sensor in rear steering assembly is dodgy.
3) 4WS ECU is dodgy (I presume that this is what Toyota mean by 'Steering Converter')

Here's what I've done so far.. Note that the 4WS fault light only comes on once I hit about 20km/h after starting - roughly when the auto transmission clicks into second - it then stays on until I turn the ignition off.

I've pulled most of the interior out of the car in search of the ECU (but haven't found it yet)
Fiddled around with the 'sport' and 'revs 2ws' buttons - there is a lag between toggling the buttons and the LED lighting on the dash, so I figure the signal must be going somewhere on the way, maybe the ECU isn't completely poked..
I've pulled out and cleaned up the speed sensor from the front left hub - it had a fair bit of crud on the business end of it, and was generally filthy with brake dust on the outside. I plugged a multimeter on it in AC mode, and could see a voltage generated when I swiped a ring spanner over the sensor end. I bolted the sensor back into the hub, and let the car idle in gear so that the left rotor spun up, and again could see the AC voltage across the sensor when the hub was turning, so I think the sensor is probably okay. Took it for a ride re-assembled (just in case it was the crud causing the problem), but still saw the fault.
I've pulled the position sensor off the rear steering and shifted the sensor arm around a bit - The motor moved very briefly at maximum throw in one direction, but not at all otherwise. So I think the motor is probably okay, but the sensor is not off the hook yet.

My questions are:
1. Does anyone know where to find the 'Steering Converter' or 4WS ECU in a Curren or Celica of this generation? A friendly auto-electrician suggested going over the circuitboard with a magnifying glass to spot ring cracks or dry joints, but didn't know where to find it to start with.
2. Did my test on the speed sensor prove anything useful?
3. How can I test the position sensor or motor on the rear steering assembly?

Thanks for any help..

Also - I've had my rear steering box apart (chasing a different fictitious WOF failing problem), and took some photos of the inside if they're useful for anyone, or need to be added to a FAQ or something (none of the specialist steering outfits I talked to in Aucks had any clue what was in there)

[Mr.Phreak]

1. Does anyone know where to find the 'Steering Converter' or 4WS ECU in a Curren or Celica of this generation? A friendly auto-electrician suggested going over the circuitboard with a magnifying glass to spot ring cracks or dry joints, but didn't know where to find it to start with.

Vague recollections they're behind the rear passenger side trim below the window

[NakiCurren]

Top marks Mr.Phreak!

There are two units - one is labelled 'Steering Control' and the other 'Steering Driver'. They are tucked up under the steel behind the passengers trim in the back seat - Below the window, and towards the back from the speaker.

In typical Toyota fashion, you have to pull most of the back of the car apart to get to them, but once you find them, at least they're labeled!

Mine look mint - I even have good copies of some Japanese dude's fingerprints on the cases.

I'm going to break out the magnifying glass tonight and go over the circuit boards, but I think it's most likely the rear sensor that's playing up..

[NakiCurren]

Fixed it. There's nothing wrong with my sensors or steering ECU. The ECU fault codes were 22 and 24.

180,000km is enough work for the main RWS motor to chew through most of it's brushes..

Where does all that used up brush dust go? Nowhere.. it just hangs around inside the motor housing. Eventually enough of it gathers to provide an alternate path for the power to go - unfortunately one that doesn't involve turning the motor, and there's your fault.

The fix is to pull the cover shield off the RWS, unscrew the motor housing on the passengers side - you can do this with the drive assembly still on the car, but it's easy enough to use a screwdriver to undo the four bolts that hold the drive assembly to the RWS housing, and easier to clean it up and re-assemble the motor on your bench. Clean all the crud out of it with a toothbrush and compressed air, and _very_ carefully reassemble the motor. I used twisty tie things to hold the brushes in while I put the core back in - you can get the springs back out with a magnet if you drop 'em down the hole , and you have to watch that the magnets in the housing don't pull the core back out to a point where the brushes pop out again as you're sliding it back over the last bit.

In the end it was only a 20 minute job to fix. It's a bit fiddly, but cheaper than a new one from Toyota!

Replacing the $5 brushes would be a more 'proper' fix - there's not a whole lot of brush left on mine - maybe only a third, but that's probably another 40-60 thousand km's worth. At least I'll know what the problem is when it dies again eventually.

I'd recommend looking inside your current unit before replacing it with a secondhand one (if you can even find one) chances are extremely good that any secondhand motor assembly will be heading the same way, so save yourself a few $ and get your screwdriver out. There's nothing that you can really screw up by pulling the cover off (it feels stuck because of the magnets and O'ring - just be firm with it.)

Hope this helps someone else fix theirs!

[Perky]

Excellent forensic work there -- and a useful description of the fix. I guess you're the 4WS guru now.