Steering control My ls 400 1991 . After speed 120m/h I feel Loss of steering control spiceial When driving between the hills or by the barriers . can you help me ............

in limp mode ---have scanned for trouble code---you have elect power assist motor mounted under dash to steering column also known problem with the knuckle at rack failing check fuses relays and wiring circuit

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If you feel it in the brake pedal and/or steering wheel you have a bad brake pulsation in the front brakes. Just replace the rotors as having them turned or machined will make them warp sooner due to the loss of material from machining. More cost effective to just replace them. If this vehicle has a 4 speed automatic......shift down into D to hook-up to the engine thru the transmission to help slow the vehicle down long hills like mountain driving. GET IT OUT OF OVERDRIVE TO SAVE THE BRAKES.
Hope this solves your problem.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/michael_2496c4f07ad24453

Your vehicle has electric power steering !
The Electric Power Steering (EPS) system reduces the amount of effort needed to steer the vehicle. The system uses the power steering control module (PSCM), torque sensor, power steering motor rotational sensor, power steering motor, discrete battery voltage supply circuit, and the GMLAN serial data circuit to perform the system functions. The PSCM and power steering motor are each serviced separately from the steering column assembly. However, the motor rotational sensor is serviced as part of the power steering motor, and the torque sensor is serviced as part of the steering column assembly. The PSCM also monitors vehicle speed from the engine control module (ECM) via the GMLAN serial data circuit. At low speeds more assist is provided for easy turning during parking maneuvers. At higher speeds less assist is provided for improved road feel and directional stability.
Stability System Indicator The IPC illuminates the stability system caution indicator when one or more of the following conditions exists. The EBCM sets any one of many VSES-disabling DTCs. The EBCM sends a serial data message to the IPC requesting illumination.
Traction Control System Indicator
TRAC OFF The instrument panel cluster (IPC) illuminates the TRAC OFF indicator when the following occurs:
?€¢
The electronic brake control module (EBCM) inhibits the traction control system due to a malfunction in the traction control system. The IPC receives a serial data message from the EBCM requesting illumination.

?€¢
The Body Control module (BCM) detects that the traction control switch has been pressed (signal circuit is low). The Body Control module (BCM) sends a serial data message to the EBCM in order to disable traction control. The IPC receives a serial data message from the EBCM requesting illumination. The BCM sends a serial data message to the radio in order to activate an audible warning.

Your best bet is to take it to a ASE certified an qualified repair shop ,that has the diagnostic tool to fix this problem .

Your PS pump is fine.

This vehicle has:

Variable-assist power steering: A power steering system that uses valves and speed sensors to vary the amount of steering assist according to engine or road speed. At slow speeds more steering assist is delivered and steering the wheels is easier; necessary for parking, etc.. At higher speeds, steering assist is reduced and more steering effort is required to steer the car, giving the driver greater feel of the road. Also known as Speed-sensitive power steering.

Loss of current to the magnetic coils would cause a loss of power assist at low speed. Coil resistance can be checked with an ohmmeter, and should read about two ohms. An infinite (open) reading indicates a bad coil (requires replacing the rack since the coils are not serviceable). Checking for shorts between both sides of the coil assembly and rack housing is also recommended.

Best wishes

You have a gas pedal your suppose to use that to drive.cruise control is designed to be used at highway speeds for longtrips. Do not use in bad weather like rain or snow. Your using it for steep hills and may have other issues going on causing the power loss. May need a tuneup and check hoses under the hood for damage

Saw this on a Lexus user club site ---

• Vehicle Skid Control (VSC) senses the onset of loss of lateral traction and helps the driver stay on track. Input from four wheel-speed sensors, a yaw-rate (directional) sensor, a deceleration sensor, and a steering-wheel-angle sensor is communicated to the VSC computer. The system has the ability to reduce power and to control the brake actuator. Working with both ABS and TRAC, the VSC system helps the driver to compensate for loss of lateral traction, which can cause skids and loss of vehicle control. Lexus Vehicle Skid Control (VSC) is an electronic system designed to help the driver maintain vehicle control under adverse conditions. It is not a substitute for safe driving practices. Factors including speed, road conditions and driver steering input can all affect whether VSC will be effective in preventing a loss of control.

However, it appears Lexus owners who have reported this sort of problem did not have to do anything to fix except - things like .. uncap gas cap and put it back, remove battery leads for about 10 minutes and put back, tighten air filter hose ...all wierd.

Have you checked your owner's manual ?

some power steering system is computer control. if you disconnect battery the control module have to be program.the control module uses vechicle speed sensor and steering wheel rotation sensor.to operate an actuator in the power steering pump to control pump pressure and steering assistance.

Problems with electronic variable-assist systems include all of the same things that can go wrong with a conventional power steering system (leaks, center wear in the steering gears, pump & hose failures, etc.), plus problems with the control electronics including the vehicle speed sensor circuit, the solenoid valve and control module. Accurate diagnosis, therefore, is essential to minimize warranty returns. Most of these systems provide diagnostic fault codes that can be accessed with a voltmeter, test light or scan tool to pinpoint the nature of the fault (if the fault is electronic rather than mechanical or hydraulic).

If power to the solenoid or control valve actuator is lost, the valve keeps the bypass circuit closed so full power assist is provided under all driving conditions. The only indication of trouble, therefore, might be a loss of road feel and/or increased steering sensitivity at highway speeds.

It’s important to remember that variable-rate power steering only reduces the amount of pressure that reaches the steering gear at higher road speeds. The only way it could reduce power assist at low speed would be in the unlikely event the actuator or solenoid valve failed in the open position. This could cause a noticeable reduction or loss of power assist.

On GM’s Magnasteer racks, loss of current to the magnetic coils would cause a loss of power assist at low speed. Coil resistance can be checked with an ohmmeter, and should read about two ohms. An infinite (open) reading indicates a bad coil (requires replacing the rack since the coils are not serviceable). Checking for shorts between both sides of the coil assembly and rack housing is also recommended.

The system does have self-diagnostic capability, but there is only one fault code: C1241 (Magnasteer circuit malfunction). The code is set if the module detects an open or a short in the coil circuit. If this code is present, the Magnasteer system is disabled and will not vary the steering effort as vehicle speed changes. The C1241 body code can be read with a Tech 2 or equivalent scan tool. The Tech 2 tool can also be used to perform a Magnasteer function test. The test varies the current to the coil so you can check for a change in steering effort when turning the steering wheel.

Replacement racks for variable-assist power steering applications are available with or without an EVO control solenoid. As long as the original EVO control solenoid is working OK, it can be removed and installed on the replacement rack to save your customer a few bucks. There’s no need to replace the whole rack if only the EVO solenoid valve is defective.

On GM Magnasteer applications, the whole rack must be replaced if the rack or control unit is defective because the Magnasteer unit is part of the rack. Handle with care because the permanent magnets inside the Magnasteer valve assembly and connector are fragile and can be easily damaged.

Good luck and hope this helps you understand the Steering system on your STS to save you some money on what to look for and what to look out for if your going to have a auto shop repair it. Such as the Valve is replaceable and it may just be a bad wire connection.

Run the car from the top of a hill and let it coast at your whining speed. Put it in Neutral, does the whine disappear?
If not its in the drivetrain (wheels, driveshafts, tranny)
Very unlikely to be the timing belt. If it appears at a fixed speed then its drivetrain, if it whines at fixed revs its the engine.
Most likey the transmission I fear....Tires will also make loud whining noise too though...