fi-How does the air suspension system work on Tesla?

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Understanding the air suspension system on your car, can save you a lot of hassle and costs. Below, we look at the system's components, how it works and any weaknesses that are important to be aware of. Maintenance tips are given along the way.

The graphic illustrates the air suspension system on a Tesla X. There is not much variation to the Tesla S. Only to notice is the placement of the valve block, on the first generation S, until November 2014, where it was located some distance in front of the compressor. On later Tesla S and Tesla X models, the valve block is located together with the compressor in the front (points 2-3 in the graphic).

Disclaimer

Teslasuspension.com is not responsible in any way for actions you take as a result of this text. Work on all types of air pressure systems requires caution and that you familiarize yourself with the car manufacturer's instructions. Always also follow standard safety instructions for working on a car. 

Content

1. Type of system

2. Air pressure

3. Sensors

4. Overpressure and 'exhaust' valve

5. Nitrogen and dryer

6. Wear over time - MOISTURE

7. Wear over time - LEAKS

1. Type of system

Tesla's air suspension system is a 'semi-closed' system. That is, it depends on air from the outside, to function optimally. Basically, however, the pressure system can be considered closed. It has its own reservoir/tank under pressure - point 1 in the picture above - where compressor (2) may collect air, and then distribute this via the valve block (3) and air pressure lines (4) to the shock absorbers (5-8). When you manually adjust the height/air struts on the screen inside the car, and things are working properly, it is from the reservoir tank, and not the environment from the outside, that you draw/fill air from/to.

2. Air Pressure

 
If you gonna pressurize the tank 'manually', i.e. without the Tesla's toolbox, it is most common to fill up to approx. 7-8 bars. Next, you try to get the car's compressor to take over, for further filling and adjustment. It is possible to use the car's compressor to fill everything up. In any instance, one must be very careful, so that the engine does not overheat. The most common is to let the compressor run in 30-60s intervals. Easiest way to interrupt is to put the air suspension in service mode in the screen manu, pull out the fuse (at least on S facelift and X models - see below for location), or in some cases simply open the door.

The actual pressure in the air struts varies between approx. 7-9 bars. When height adjustment is set to 'Low', there is approx. 7 bar pressure in the bellows. At 'Very high', there is approx. 9 bars. If the air suspension is decended to 'low' position, air is supplied to the tank, increasing the pressure to an estimated 13 bar. We thus get a working pressure in the air tank of the Tesla S/X of between 9 (air suspension 'very high') to 13 bar (air suspension in 'low' position). Note that the pressure sizes we operate with are subject to uncertainty, and must be regarded as estimates.

If the car's compressor is disabled for some reason, and the car falls down at the front for instance - and is due to minor leaks in lines or because the valve block does not work properly, or maybe the sensors are failing - it is possible to use an emergency kit to refill each bellows. The car can then be driven again. A simple external compressor (a battery-powered one is normally up to the job), is required.

3. Sensors

Compressor and valve block help to adjust the air struts according to what sensors detect of height, surface and load. The main sensors are connected to the height adjustment mechanism on each shaft. In picture 1 we see the height sensor on the front of the Tesla X. Pucture 2 shows it on Tesla S rear:

The sensors detect the height of the car. For example, if it is too low, signals are sent via an electronic control unit (ECU) to the valve block. The compressor can - if not necessarily - starts to run, and air / pressure flows from the tank into the bellows so that the car is raised.

Maintenance tips. Joints from sensor bracket to link arm, is susceptible to rust and can become stuck. Lubricate them occasionally. This way, you may avoid for instance that the rear air struts get stuck in a given position, while the front ones work as normal.

The basic pressure settings are registered via the menitoned ECU (Electric Control Unit), which switches the compressor on/off by the relay. Together with signals from the electrical connector to the valve block, it regulates the air flows to/from the air struts or the pressure tank, depending on where it is needed. It all works as a kind of pressure sensor, we may say. If there are discrepancies between registered pressure in the system and what is electronically plotted, the compressor and valve block will work to equalize it.

Basic settings of pressure may possibly also be different on similar types of air struts. Plus editions of the 2013-15 S model, for example, provide a stiffer suspension experience, which may mean that the pressure is set higher at the same levels, than the standard edition. But there is uncertainty here. It is probably more likely that the 'tighter' driving experience on plus versions, is due to stronger bushings and tie rods, rather than stiffer air struts. In any case, you cannot adjust the basic pressure settings yourself.

4. Overpressure and 'exhaust' valve

Overpressure in the system is solved as follows: we can imagine that you are driving on a huge dump, which presses the bellow in the air strut on one side hard together. If it is too much for the system, the air must find a way out. On the valve block there is an exhaust valve / 'out' valve, which opens. The air is squeezed out. You occasionally hear this in the form of a kind of 'woooooosh' blowout.

In the opening image of the video below, we see a valve block from Tesla S, first generation models (in principle similar on other S/X models). On the right, with yellow arrow, is the electric connector. The red arrow, the one on the far left at the bottom, shows the exhaust valve. The video briefly shows where this "out" tube is heading. Supplementary subtitle, you can turn on via the settings wheel icon at the bottom.

There can also be other types of failure in the 'exhaust' valve, e.g. that it does not close properly. This can lead to air loss, the air struts fall down, and an error message appears on the screen. The compressor will probably not start, which is good, because the air that would be pumped, would have disappeared through the exhaust valve. It prevents the compressor from getting burned/damaged, and also stops the air struts from falling even further.

Also note that the compressor's return valves, which take care of the air 'returning' from the bellows to the tank, may fail. The pressure still has to go somewhere, and that is out through the exhaust valve. The 'Wooooosh' sound can then become relatively powerful. In such cases, the compressor usually needs to be replaced.

To sum up, the system is not closed, but 'semi-closed'. In addition to an opening out, compressor can also draw air in from the surroundings. On older cars, high intake is more common than on new ones. After a number of years, and many episodes of overpressure etc., the pressure in the tank will naturally decrease. The compressor counteracts this by refilling outside air so that the set ground pressure is maintained.

5. Nitrogen and dryer

In our part of the world (Scandinavia), with large temperature fluctuations, wet and cold wintertime, such a partially open system presents particular challenges. The air taken in can be very humid and cold. When it turns to minus, moisture can begin to freeze in valves and connections.

To remedy this, Tesla's air suspension system has two answers. First, it is not clean air that is initially filled on the system, but nitrogen. This has a higher freezing point, and up to a certain point, will neutralize the ingress of moist air.

Secondly, compressor has a dryer. On most variants, this is the cylindrical part, above the electric motor. The elements within it, are filters and small silica balls, which draw moisture out of the air. Excess moisture, the compressor gets rid of through the same exhaust valve on the valve block as mentioned above, and we also often hear this as a "wooooosh", which is completely normal.

6. Wear over time - MOISTURE

On newer cars, there are little problems with this system. When we have passed tens of thousands of miles, and the vehicle is usually 5-6 years old, wear and tear damages often occur. The first natural reaction to the system's operation is that the nitrogen leaking out of the exhaust valve is replaced with ordinary air.

Maintenance tips. For older cars, and where the air system is tight/in order, flushing/replacing nitrogen gas in the system can be preventative. This is done at Tesla Service Centers, or at a few private workshops such as Bosch Car Service / Bilexperten (in case of Oslo, Norway).

Replacing nitrogen with outdoor air is not any crisis. Problems usually arise when this coincides with the dryer in the compressor no longer works optimally. Over time, or under exceptionally high moisture loads, the absorbency of silica balls will be lost and stop drying the air properly. Below is a Youtube video showing the change of filters and silica balls on a dryer:

Compressor now must work a lot to push excess moisture out through the exhaust valve. The sound of 'woooooosh', and compressor running, tends to become more frequent. And it's a self-reinforcing process, where the original nitrogen in the system is 'eaten away' in favor of outdoor air.

In the summer, this usually goes smoothly. However, with freezing temperatures and vivid fluctuations in winter, valves and connections can freeze. Most susceptible is the valve block. Signals from sensors and basic settings are blocked by valves that do not open. Distribution mechanisms internally in the valve block can also break, in the worst case.

Fortunately, one might say, at this stage, the car often gives the message that something is wrong: "Compressor deactivated/air suspension adjustment not available", comes as an alert. Or a yellow/red car with an arrow underneath, appears in the screen, or the fuse/relay for the compressor breaks.

Maintenance tips. Also check the electrical connector to the valve block. In the event of an unusual amount of moisture in the surroundings, corrosion can form. Then nothing works anymore, and you may find, for example, that the air struts rise at the rear, while the front falls all the way down.

In many cases, things resolve when you get your car into a temperate zone. Nevertheless, frost damage to valves, collets, and distribution mechanisms, may have destroyed the valve block. In addition, compressors are not built to run as much. Constantly working on getting rid of moisture and equalizing pressure, makes the electric motor run hot, and it can be destroyed.

7. Wear over time - LEAKS

Leaks are at least as big a problem as moisture on Tesla's air suspension system. In most cases, it is the air struts that fail. The air pressure lines are very solid, but of course holes can occur if, for example, they fall out of the clips and rub against something over time.

'Soap spray test' will reveal if there is a problem with the air pressure lines in the front. Similarly, connections to the valve block and compressor, and each individual air strut, can be examined. In some rare cases, leaks occur in the air pressure lines on the way to the rear air struts and cannot be detected visually, since they are encased in the bodywork.

The 'tape test' gives a fairly certain indication, if the air struts are leaking. Via the control panel, put the air suspensions in Service mode overnight (preferably longer). This closes the valves, the compressor cannot run, and the pressure is locked.

Tighten a piece of tape between the body and wheel and see if it curls. If it does, the strut has lowered, and you most likely have a leak in the air strut.

Maintenance tips. If you see dirt and corrosion around sealing rings / O-rings on the air strut, cleaning and lubrication with silicone grease or acid free vaseline can help well, and prevent leaks from occurring (see videos below examining this issue).

There are many things on an air strut, which allows leaks to occur. The most common, is probably that the rubber in the bellow, which has been added a little textile to make it stronger, ages. Microscopic, small cracks appear, and air leaks out. Then, it will rather useless to fix sealing rings as shown below, and the leaks will not easily be detected with a simple 'soap spray test'.

      ■ A - Leakages down at the strut

Video 1: From Vigor® manufacturer

Video 2: From teslasuspension

Next is to make an assessment as to whether you should start with a rehabilitation to get rid of rust and oxidation. Remember that this does not help against worn out bellows or shock absorber. Provided these work properly, it may still be worth a try. In that case, the following video gives you a hint of what to expect.

    
■ B - Leakages at top of the air strut

Similarly, for the Tesla S pre-facelift air struts, both original and Vigor® ones, the construction is closed in form. The metal top plate sits well. Any leakage will therefore mostly be linked to the valve inlet on the side of the air suspension. Because of a more protruding construction, rust can form around the attachment (picture 1) and/or the the retaining valve can fail (pictures 2-3). The X and S facelift models are not so affected by this, as they do not have retaining valves. But leaks can still occur around the valve inlet due to wear and tear.

For some Tesla X models, seepage in of sand/salt brine, along the upper part of the cuff of the front air struts, is a peculiar problem. The strips around the cuff, does not tighten well enough. Years of such seepage in, which may also freeze in the cold, can destroy the air strut. Both the sealing rings below, and the rubber bellows encased in the rolled aluminum cylinder directly above, may be damaged. The top of the air strut can also be exposed on its own, with corrosion intrusion around the sealing rings and leakage as a result. A soap spray test will reveal this, but you have to screw a bit to get access there.

You can easily check if you have an inflow of sand/salt brine, by pressing the cuff against the strut. There is about one cm of airspace here, and the cuff should be reasonable soft and give way. If you get a lot of resistance, something is wrong. Once you're up and running, it's also beneficial to clean and rust-protect the transition between air strut and lower legs (see picture 2 above). Sealing the transition around the strips at the top can also be a good preventive measure (picture 3). And the procedure for loosening the lower part of the cuff, you can watch here:

Maintenance tips. Cut off the metal strips on top of the cuff, pull it down, and use compressed air or the equivalent to blow away the sand/salt brine. Alternatively, open up the cuff from below and clean as best as you can (see video above). New metal strip at the top must be min 50cm long, and firmly tighten. Consider sealing the transition with tec7 or equivalent. Rust protects the transition between air strut and lower leg.

Leakage in the air struts can, in the same way as with moisture, disrupt the entire air suspension system. Now, the compressor and valve block can withstand a great deal. But if the compressor must constantly draw in external air, to equalize pressure due to leaks, it quickly runs out of power, and the air tank runs out of nitrogen. A possible moisture problem can thus accelerate, and if it turns into winter, it also puts the valve block at risk. So, on these older cars, it's wise to address the problem, as soon as it occurs. Then you minimize the damage.

Summary

Air suspension systems on Tesla can seem complex, and difficult. Some are of course lucky, and do not experience problems of any kind, even if the car has driven well over 150' miles. For most people, however, problems will arise, either with moisture or leaks, when the car reaches 5-6 years of age. However, if you pay attention and change parts as they fail, the costs for most people can be affordable. However, this requires some effort, and that you pay attention and understand the system that keeps your car soft and safe on the road.