DanielDD

iTrader: (1)

Guys. My GS400 requires a high steering effort at low speeds. Since I just got it, I don't know a whole lot about it, so I need your help. Is there some sort of valve or solenoid on the power steering unit that modulates the pressure so that in parking lot conditions the steering effort is light and then firms up when going at cruising speed?

Mine always seems to be quite firm whether I'm negotiating a parking space or cruising down the road. It requires both hands to get in and out of a parking spot. There is no pump whine and I have plenty of fluid.

I'm thinking I have a stuck solenoid or no signal to the solenoid, but I don't know these cars enough yet to really have an informed guess. So, can you help me out in troubleshooting this?

Also, is there any online Lexus service manuals someone can point me to?

MasterKwan

There is and it's super expensive. If you open the hood, look down at the alternator. Above the alternator is the PS pump. On the side of the PS pump, where the high pressure hose connects, you'll see a cylinder that screws into the high pressure line banjo. That's the pressure solenoid that lets the ECU control the PS pressure.



44170G 4417030120 VALVE ASSEMBLY, SOLENOID (FOR POWER STEERING). VALVE ASSY, SOLENOID UZS16# $494.14 44


TIS Toyota Information System.

$15 for 3 days access and you can download all the PDF's.

I'm installing a 97 SC400 PS pump on my car. Doesn't have this solenoid. $160 reman from Napa. It is NOT a plug and play swap. I have to fab the high pressure lines to make it work.

DanielDD

iTrader: (1)

Thanks MasterKwan.

I will do some investigation with regard to the solenoid before I decide that it is indeed bad. It could be something simple. Maybe it got disconnected or its not receiving the proper voltage from the power steering module.

Since I haven't found any threads in the forums of past members having any problems related to wht I am experiencing, I have to suspect the input to the solenoid may be the root cause -- as I sure don't want to pay for something that I may not need.

Appreciate the parts diagram and a source for repair information..

MasterKwan

I'm sure Lexus has a trouble-shooting guide. The solenoid uses a 32 mm wrench (which I happened to have left over from a BMW job). Might be worth unscrewing it and seeing it it's sticking out or not. When I unscrewed mine, it was sticking out 3/8-1/2". I assume that's the resting position.

Looking at the schematics, this solenoid is driven by the "PPS ECU" which gets power, ground and a speedometer signal from the cluster. The wiring is marked "Sol+" "Sol-" which makes me think the motor is spin out and then spun back in again to control the pressure. Perhaps less a solenoid and more like a stepper motor.

http://www.autospeed.com/cms/A_110778/article.html

Interesting story.

DanielDD

iTrader: (1)

Enjoyed the article you linked to. I'm guessing the LS400 has a different steering setup than the GS series, but it was an interesting read, nonetheless.

I just happen to have the same wrench as I already have two BMWs (E39 & E31). 32mm is a big wrench. Wondering if I'm going to have enough clearance to break the solenoid loose with it on the car. Guess I'll find out in the next day or two. Prior to removal, I'm going to try to determine if there is a voltage signal going to the solenoid. I believe when you turn the key to the ON postion, it energizes the solenoid initially. If I don't get this, I will apply 12v directly to the solenoid to determine if I hear and audible click. IF not, then I will remove it and perform further analysis.

MasterKwan

Sounds like a good plan. The solenoid sticks out pretty far so, you should be able to get on it. I have the radiator out at the moment so, I probably have more clearance than normal. It's not that hard to dismount. Just messy. A nut on the front and 2 bolts into the block on the backside of the pump.

In my case I'm eliminating it because I don't have room for it. It intersects the framerail (engine isn't in a GS anymore).

ThomasGS4

iTrader: (19)

Just out of pure curiosity, what color is your PS fluid?

DanielDD

iTrader: (1)

slightly red....

I couldn't immediately tell by looking at the reservoir, but when I unscrew the cap and look at what is coming off of the level indicator, it is slightly red. Since it has always been serviced at the Lexus dealer I would think they would fill with the proper fluid and not the clear power steering fluid.

DanielDD

iTrader: (1)

Update....

I got a 2 day subscription to the Lexus/Toyota TIS. This is a great way to get the specific documentation on a particular subsystem of your car. Very complete, lots of pictures and diagrams, both mechanical and electrical. Well worth the $15 dollars spent.

1st thing I did was checked the ICU-IG fuse under the dash, on the driver's side kick panel. Fuse checked good.

Next, I removed the air box so I could access the power steering pump directly. I disconnected the 2 pin connector from the pump solenoid and measured the resistance of the solenoid. It should be between 6 and 11 ohms. Mine was 7.8 ohms.

Next, I checked the operation of the PPS solenoid. I energized the solenoid using the car battery for a very short interval. Documentation states not to apply voltage for more than 30 seconds to avoid burning out the solenoid. Application of 12V I could hear the solenoid "click", so accordingly, it tested good.

Next, I removed the PPS ECU connector under the driver's side dash. You have to remove the black trim piece under the dash. A couple of screws, pinch the securing tab and it easily comes off. With an ohmmeter, check pins 1 & 6. It should be infinite. Same for pins 2 & 6, should be infinite (open circuit). These checked good as well. What this test does is determine if you have a short between ground and one side of the solenoid. An open circuit means you have no short. On to the next step.

Next, I inserted wires into pins 2 & 6, inserted the connector back into the PPS ECU, connected the wires I inserted into the ECU to my digital voltmeter and set it to DC volts. Turned the car on and I read 0.181 volts. The spec is 0.160 to 0.200 volts, so I'm within spec.

Next, we go for a drive, drive car up to 62 mph (100km/hr). Voltage should drop to 0.010 - 0.070 volts. Mine was 0.135 volts. A noticeable difference. Now, I can't claim victory at this point because I don't know for sure if this is the issue, but it all points to the ECU as the culprit. I found one on Ebay for $20, so I ordered it last night. I can't confirm whether this will fix my issue until the unit arrives and I try it.

Stay tuned.........

MasterKwan

Now that's how it's done.

pdxgs

iTrader: (7)

If it's not the ECU, try checking the condition of your steering rack bushings. Changed mine out with poly bushing and it made a noticeable difference in easing the steering effort.

marshun

currently having the same problem. anyone else trouble shoot this?

marshun

so my pps ecu has a reading across pins 2 and 6. bad ecu?

my ps solenoid reads an 8.8. i know it says 6-11 ohms according to this thread. im wondering if adjusting that will help to keep another ecu from burning out as well (assuming that mine is actually bad)

eicca

@DanielDD were you ever able to reach a conclusion?

I have the same symptoms and went through the same process with practically the same results. Everything checked out fine except voltage while moving. I don't know what idle reading is supposed to be but I got 0.18v. The instant I started moving it would jump to 0.24v and decrease linearly to 0.13v at 65mph.

If lower voltage is supposed to equal stiffer steering, I would assume that low voltage at stop isn't exactly helping the situation if that means restricted flow to the rest of the system.

DanielDD

iTrader: (1)

Nope. No conclusion. I sold the car to my son. The problem is still there. He took it to the Lexus dealer last week for a good top to bottom maintenance investigation. One of the things they were going to look into is the hard steering issue. Don't know if I mentioned it earlier, but I did replace the steering ECU and it did nothing to improve the steering effort...