'94 TT Intermittent Power Steering Issue

Hey peeps! Long time no Post! :banned:

Just to mention firstly, my Zed is a '94 model TT, and it has the electronic (super) Hicas, rather than the original hydraulic Hicas that we all know and love(to delete) :rofl:
Anyway, just in case that has anything to do with my diagnosing, i wanted to mention that at the start. (eg, no longer has a hicas computer to diagnost in passenger footwell like older models)

Problem is intermittent power steering going off and on. More often off than on. Will remain off while stationary, and at speed.
An occurrence of it coming back on by itself might be after driving for an hour or two. But then after leaving overnight, it's gone again.
So far it looks like it spends more time not working than it does. Stationary or speed doesn't factor in if it's working. Possibly heat might be related to the issue, as when it does come back on, it's usually after a long drive.

I've confirmed the mechanical side of things (pump, hoses, belts, fluids) are all fine, and have also checked by applying 12v directly to the power steering solenoid that's on the steering rack while idling, and sure enough the power steering starts working again perfectly.
I've also tested via ConZult that the power steering switch is triggering properly when you turn the steering wheel at idle, so the ECU is getting correct information that the wheel is turning. Also the speedo gauge works fine as per normal.

So the issue appears to be directly related to power supply getting to the p/s solenoid. Where does that power supply come from or how is that switched?
I've heard from different areas that the power supply is fed from the speed sensor on the gearbox, then via the dash (speedo?) and then to the p/s solenoid?
Not sure from here, but i'm trying to back-track to diagnose further. Any further tips to help isolate the fault would be great!

...Also, just one extra (and possibly dumb) question, but would there be any issue with adding a separate and permanent 12v feed direct to the p/s solenoid only while engine is in a running state? Genuinely curious about this. Would there be any harm in this as a possible bypass for 1 less failure point in future? Or is that power feed that comes to it via wherever it comes from, variable or switches during conditions?

Thanks in advance peeps!
Benny_C :zlove::br:

 

Hi Benny,
With respect to your last query...
The Power Steering assistance is ideally proportional to the road speed/steering load at any given point in time (as you know), therefore, it would be hugely questionable if such assistance was applied when unnecessary and/or not required/expected.
It is also usual for the Steering Gear ratio in unassisted Steering Boxes to be less sensitive to small input from Steering Wheel and/or road surface irregularities(thus providing the "feel" that is transmitted back to the Driver, at any given time).
Hope this is somewhat helpful Mate.:zlove:

 

Thanks for that! Just to confirm what you were asking, i can confirm there is no voltage getting to the connector at the power steering solenoid. So wherever that power feed comes from, appears to be not supplying any power at all. This is ideally what i need to find out. Whether this is a component of some kind, or a new speed sensor from the gearbox? I don't know how to diagnose that side of things...

Also, that makes perfect sense where that 12v feed switches off at speed (80kph as your example), for the variable assistance state change. So in this regard, a 12v solenoid feed bypassing would be harmless to the mechanics/electrics of the car itself, but more of a safety/comfort factor to have less power assistance at highway speeds. (also like Lloyd mentioned in his post)

 

Is the speedo fully functional? Can you get a speed reading through conzult/ecutalk?

Is the power steering completely failing or just going into the fail safe low assist mode? In fail safe you'll still notice a difference in steering weight when stationary depending on whether the engine is running but much heavier than usual.

 

Hi Benny nice to see you back. As Fists said check if you have a speed reading on consult when moving then slowing down. Also check the wires that go into the rack solenoid as the have a habit of breaking near the rack and when you bent them to put 12v directly you may have remade the connection. But my bet if I was to bet would be a dry soldered joint somewhere and that may more than likely be on the back of the speedo p.c.b see as it can be intermittent.
Good luck and let us all know what you find.
Cheers
Dave

 

Hey Dave and Tom!
Thanks very much for the input guys! I can confirm the current normal state of the steering is the "low assist" setting. Not completely non-functioning, but not working at full assist mode. So that's where the problem lies.
Also, i can confirm the speedo is functioning perfectly in both the stock dash, and also via ConZult. So the accurate speed is getting to both the dash speedo, and the ECU. I'm thinking the problem might be somewhere from there down to the power steering solenoid connector.
I hope this isn't a noob question after my 13 years on this forum, but is there a circuit diagram or photos showing the path of the wiring from the power steering solenoid up to the dash? I'm having troubles trying to find anything helpful right now...

 

The fsm is available online.
The solenoid gets pwm'd from the controlmodule iirc.

 

Hi Benny type power steering in the tech section search bar and there is info that may be helpful.
The first one especially. It shows were the wires go and what signals you should get to help diagnose were the fault lies. Also the z32 wiki page has a great wiring diagram. Shows a power steering pressure switch and were the wiring goes. Power steering pressure switch wire is green and goes to terminal 34 on the e.c.c.s by the looks. The negative feed to that switch is a body ground. Check them both. That same ground feeds the radiator fans so just pull the temp sensor plug to see if the radiator comes on and if it does then maybe just put a multi meter into the plug earth at the sensor to be sure it,s not broken in between.
Cheers
Dave

 

Battery

Hi Benny
I had a similar problem on my old car 89 TT with hydraulic Hicas. Tried everything under the sun to fix it including swapping the steering ECU.
So the solution was either that or re soldering several connections in the gauges.

But even though I had made the changes, nothing happened untill I disconnected the battery. Must re-set something I guess.

 

Thanks everybody, for the direction and links, etc...
I'll firstly pull the gauge cluster and re-solder the joints of the speedo section. See how things go after that, then if not fixed diagnose further from the electrical diagram.

Looks like i've got stuff to do this weekend now!

 

If you've got a speed reading at the ECU then it shouldn't be a problem at the cluster, unless of course nissan changed the routing for funzies. I'd be tracing from the other end, the rack solenoid connector comes off the alternator/transmission harness doesn't it? Shouldn't be too hard to trace that back.

 

Maybe a dodgy speed sensor?? Just thinking out of the box here.

 

Just wondering if there is anything loose in the steering, like tie rid ball joints or where the arm bolts into the steering rack (under the rubber accordion boot.

I have had intermittent power steering issues in the past (drove 900km with very light steering on one trip)
A combination of replacing steering arms tightening up bit and pieces in the steering and suspension to reduce play and changing the setting on TPS, all that together seems to have stopped the intermittent light steering. I do have some power assistance at parking speeds, but not sure if I have full assistance. Seems good enough.

So I suppose I am saying, check everything?