91LS400vgb

A relative of mine just got a 91 LS400 like mine. It had a problem with stiff steering, so I took a look at it for him.

The power steering showed no signs of leaks; the only issue I could see was that someone overfilled the reservoir - no biggie.

I started by putting the car on jack stands and loosening the Solenoid valve on the rack. Prior to loosening it, I marked a line between the solenoid and the housing as a reference. I had a very difficult time getting it off but I finally did. I posted how I did it here ---> https://www.clublexus.com/forums/ls4...tem-diy-4.html

Anyway, there was a lot of crud on the screens. I cleaned it thoroughly with brake cleaner. I gently used a toothbrush to dislodge the dirt. After I got it nice and clean, I let it dry out for a while, then I applied some ATF to the o-ring and screwed it back in until the reference lines lined up.

Since the reservoir was empty at this point, I took the opportunity to replace the low pressure hose. I refilled with Mobil 1 synthetic Dexron ATF and bled the system as per the manual (stop to stop 4 times, with rpm < 1000, pausing at extreme stops for 2-3 seconds). The steering felt great while the car was up in the air but it was still stiff after lowering it to the ground.

Next, I checked out the solenoid. Manual calls for resistance between 6 and 11 ohms; I got 7.7 ohms. Then I did the click test, and I heard the click.

So, next I started looking at the p/s ecu. I had to remove the lower panel under the instrument panel. Three screws and some clips, no big deal. As per the manual, I verified that the ECU-IG fuse was good (I knew it was ok because it also powers the door locks). Then I disconnected the ECU connector. I confirmed that there was 12v between the B+ terminal and body ground, and continuity between the GND terminal and body ground. The 1st and 5th pins go to the solenoid, and I verifed that I got the same 7.7 ohms that I got directly at the solenoid, and that neither had a short to the GND terminal.

I sprayed some tuner cleaner onto the terminals and plugged the connector back into the p/s ECU. The manual says to start the engine and check the voltage between pin 1 (SOL Neg) and GND at idle. It should be 0.32 - 0.44v. I got nothing. Hmmm.

So, I went over to my car and did the same thing. I got 0.35v. Bad ECU? I went one step further, and took the p/s ECU out of my car and put it into his car. Started it up and I got nice power steering - no stiffness at all.

Now, this is the strange part. For the heck of it, I thought I'd put the suspected bad ECU into my car, and I was surprised that my power steering was fine. I can't explain why. I did open up the ECU box to look at the circuit board, before putting it into my car, and I did not see anything obviously wrong with it.

Anyway, the problem is resolved, at least for now. I will keep his ECU in my car and see if the problem returns.

dicer

You said stiff steering?? Mine does a thing when its cold like a hesitation or like it bumps a valve and then steers, after that initial deal when cold its okay.

JimsGX

I would suggest replacing the PS fluid with Mobil1 ATF and cleaning the solenoid filter to fix this problem...


91LS400vgb,

Nice job in diagnosing your relatives PS problem...

91LS400vgb

Thanks, Jim. Dicer, I agree with Jim - try doing that first. If that doesn't fix it then you can look at other possibilities like binding steering parts, for example. Btw, when you remove the solenoid, if the fluid that flows out looks nasty, then it's possible that the rack itself is full of gunk. If that's the case you can get some SeaFoam Trans Tune to clean it out. See this link:

http://www.youtube.com/watch?v=pjId3bfMBUQ

Of course, that's going to release a lot of gunk, so you'll have to clean the screens again afterward.

sam12345

iTrader: (1)

check the screen in your resevoir. It can plug up and give you stiff steering

ck90211

Without thinking I refilled my just re-built pump/rack/high pressure hose with power steering fluid, and it felt stiffer than before. Going to drain & refill with ATF and see if it makes a difference.

justincook

My local shop suggested a steering pump flush. I reluctantly agreed... but it made a huge difference. I am back to 1-finger steering in parking lots.

mrmox

Perhaps I should ask a new question, but I cannot find a picture of where the PS ECU is LOCATED on my 1991 LS400.

Power Steering pump replaced 1/2021, leaking. Worked good.

8 months later: Stiff steering (no leaking).
Suctioned reservoir screen, no change (screen looked pretty clean to me). This was easy because I has a vacuum pump and a home-made wet vac jar.
May as well share some pictures, wish I had played with the light dimmer on the DEPSTECH USB camera but too late!
Looks like some deposits on the screen, now that I see pics close up. This was after I suctioned hot fluid out, making an effort to keep the butt end of the hose in contact with the screen FWIW.
But mostly clear.

Home made Power Steering Reservoir Wet Vac

Hard to get scale, should have dropped in a dime!
Camera Illumination light can be seen reflection off the Metal on the bottom? Or a layer of un-suctioned fluid?

Not comfortable to clean the SOLENOID screen myself, so looking for other easy fixes ;-)

91LS400vgb

The Power Steering ECU (PPS ECU) is behind the Instrument panel no. 1 under cover as seen in the following image. If I recall correctly, it's a blue colored box and says "ECU, Power Steering" on it.

deanshark

Good description on the diagnosis. Glad ya finally got it fixed for them. And yes, it is weird that the PPS ECU worked in your car and not their's. I have a problem now with stiff steering in my new 93 and I will be pulling the PPS ECU out of my parts car before it goes. In fact, I'm gonna pull every ECU I can get to without too much trouble just to have as spares.