Air Suspension in General
Having air ride problems on a Lexus LS400? If your car is around 10 years old, it's decision time on whether to stay with the air system or convert to coil springs and be done with the problem forever. Most people don't realize that an air ride system is similar to brakes and tires. It is comprised of wear items and will require multiple repairs during the life of the vehicle. These systems usually start failing approx. 7 years old, with the major more expensive parts having a lifespan of about 10 years. Unfortunately, if the root cause is not correctly diagnosed by the technician, some parts maybe replaced needlessly, or even need to be replaced more than once. Greatly adding to the cost of maintaining your vehicle. Its been our experience over the years, that only 1 in 20 mechanics are good at diagnosing an air system. While most can finally get it working after a while, the majority will just keep throwing parts at the vehicle until either they get lucky and fix it......or you run out of money.
Basic Part Strategy
The air suspension control module on the Lexus LS400, will test everything when the ignition is switched to the on position. If it sees something out of range, it will turn the check suspension message on and shut down the system.
To keep from making any unnecessary adjustments, the module(brain) will only "look" at the sensors every couple of minutes or so. When the module "looks" at a sensor, it will make a height adjustment either up or down if needed.
It will make a raising adjustment by first signaling the compressor relay, which powers up the compressor and pressurizes all the lines. It will then open up the solenoid(s) on whatever corner or corners it needs to make the adjustment to and allow air to flow into the air struts/springs.
When the desired ride height is reached, the solenoid(s) will close and the compressor will turn off.
It will make a lowering adjustment by opening the vent solenoid in the compressor as well as whatever solenoid on whatever corner or corners it needs to make the adjustment to and allow air to flow out of the air strut/springs, through the lines, through the dryer and finally through the vent solenoid on the compressor. When the desired ride height is reached, all the solenoid(s) will close.
NOTE: The Lexus LS400 has what is known as a 3 channel system. This means it only has 3 sensors. One in the Left front, one in the Right front and one in the rear. It can adjust the front individually, but because it only has 1 sensor in the rear, it adjusts the rear as an average. The one in the back is for both sides as an average. The rear solenoids are wired together, so when one gets signaled to open, the other will too.
The module is the "brains" of the system. It makes any height changes necessary based on the data from all 3 height sensors.
AIR SPRING SOLENOID
Each air spring/strut has an electrically operated solenoid that the module uses to isolate each air strut/spring from each other. The module can control the left front, right front or the rear-end independently. The solenoids act as a "gate" for air. No air goes in or out unless the solenoid is opened or "signaled" by the module. All solenoids have a 2 pin connection. Its a simple circuit of "power" and "ground".
If the module determines the front or rear of the car should be raised, the air compressor will come on, the solenoids will be opened up and air is allowed from the compressor/dryer, through the air lines and into whichever air struts/spring until the desired height has been reached. When this height has been reached, the solenoids will close and the compressor will shut off.
If the module determines the vehicle should be lowered, the solenoids on whichever air strut/spring will be opened up, as well as the vent solenoid in the air compressor. The vented air will pass out of the strut/spring, through the air lines, through the compressor/dryer, then to the atmosphere. Once the vehicle has reached the desired height, the solenoids on the air springs and compressor will close.
While these solenoids don't go bad that often, they do need to be resealed when removed.
The sensors are the eyes so to speak for the module. The sensors let the module know the height of the car.
The compressor supplies air to the air springs/struts. The compressor has air lines coming out of the dryer which go to each solenoid on each air strut & air spring. It does not matter which line goes into each hole in the dryer. You may find that the lines are molded and one line may fit better when its inserted in a certain hole, but it won't make any difference when adding or removing air from the system.
The dryer is like a common manifold. In other words, the compressor/dryer assembly doesn't know what corner(s) the adjustment is being made on, it only knows to come on when told to do so, or to vent when told to do so. Again, the module controls that by opening whichever solenoid(s).
Any air compressor produces moisture, so a dryer is needed to trap and absorb the moisture BEFORE it gets to the struts/springs. The dryer consists of moisture absorbing silica gel beads and 2 metal plates. These plates can rust very badly and actually turn to powder. This powder can then clog up the dryer first and then make its way to the vent solenoid and clog it up also. So now what started out to be a dryer problem, has turned into a compressor and dryer problem.
The dryer is the only part of the compressor dryer assembly that is sold separately from the dealer.
COMPRESSOR VENT SOLENOID
The vent solenoid on the compressor is used as a "vent to atmosphere" solenoid. When the module gives the command to vent the car down, this vent solenoid and whichever solenoid on the strut/spring that the module needs to vent, opens up and vents air out of the system. If there's any moisture in the general area of the compressor, the moisture will find its way to the vent solenoid just from gravity. NOTE: The piston inside the solenoid is metal, so it can't deal with moisture very long before rust starts setting in.
The compressor is turned on by way of a relay. This relays only job, is to power up the compressor
With age, the rubber air bladders on the air struts & springs will dry rot and eventually leak air. The leak will almost always be "on the fold of the rubber". This is where the rubber folds over itself and that area changes with vehicle height. Upon inspection, you may not see any visible cracks until the height has been achieved where the car has sat most of its life. Once this area has been found, cracks will magically open up on the fold.
Early in the stages of a leak, the air springs & struts will only leak while being driven. Remember that the system is all automatic, so if there is a leak, you probably won't realize there's even a problem until one of two things happen:
#1 The leak gets so bad that its leaking more air out than the compressor can put back in.
#2 The compressor is damaged and can't keep up with the load.
As was stated before, in the early stages of a leak, it will only leak while being driven. As time goes on, you will probably notice the car going down one or more nights in a weeks time. The number of days the car is down will increase as time goes on.
Even driving the car, the leak will get progressively worse and eventually to the point where you can't drive the car.
ANY air compressor produces moisture. When a system has a leak and the compressor has to run 2-10 times more than it would normally, the compressor will produce 2-10 times more moisture than it would normally.
In time, the moisture absorbing gel beads in the dryer lose their ability to remove the moisture from the incoming air. Moisture is then able to make its way back to the rest of the system. Turning every low lying area into a moisture reservoir.
The dryer also turns into a reservoir for water. In other words, when the compressor vents, moisture will be blown back through the compressor. This is very hard on a part that was designed to be operated dry. These problems include, but are not limited too:
Swelling of the piston rings, which makes the electric motor have to work that much harder to do the same job and increases the heat made by the compressor, which is hard on any sealing o-rings in the high heat area.
Rusted and corroded compressor vent solenoid
Rusted and corroded end plates inside the dryer
Rusted and corroded intake & exhaust valves in the compressor
Damaged armature & brushes
THE SOLUTION TO YOUR AIR SUSPENSION PROBLEMS
Install a Lexus LS400 Air Suspension Conversion Kit!
Put Coil Springs, made by the worlds Best spring manufacturer, along with the best struts known to man. What you wind up with, is the absolute BEST conversion kit you can buy!
Installation requires no drilling, cutting or welding and even comes with easy to follow illustrated instructions, to walk you through the installation process. A toll-free tech line is offered in case you or your mechanic gets stuck on something during the install.