Air suspension is what makes premium saloons and SUVs such as the Mercedes-Benz E-Class or S-Class, the Audi A6 and A8, the BMW X5, the Range Rover or the Porsche Cayenne ride so smoothly and always keep the same height. When something goes wrong, the car usually warns you before it ends up sitting on the ground. In this guide we go through the most common symptoms, how to find the cause and which part you should replace.
How air suspension works
Instead of steel springs, the car rests on air springs (rubber bellows filled with air) or on air struts, which combine the air spring and the shock absorber in a single unit. The rest of the system consists of:
- The compressor, which produces the compressed air, with its air dryer (removes moisture) and its power relay.
- The valve block, which distributes the air to each wheel.
- The ride height sensors, which measure the height at each corner.
- The control unit, which decides when to raise or lower the car.
When one of these parts fails, the others have to work harder. That is why it is important to find the cause instead of only replacing whatever broke last.
7 signs that your air suspension is failing
1. The car is lower in the morning
This is the classic symptom: in the morning one wheel, one axle or the whole car sits lower than when you parked it. It almost always means an air leak in an air spring, an air strut, a fitting or the valve block. If only one corner drops, the leak is usually on that side.
2. The compressor runs more than usual
If you hear the compressor often, or it runs for a long time, it is compensating for a leak or struggling to reach pressure. A compressor that never rests overheats and wears out, so act early.
3. A warning on the dashboard
Messages such as “Airmatic: visit workshop”, “Suspension fault” or “Suspension: reduce speed” appear when the control unit detects heights out of range, filling times that are too long or an electrical fault. The first step is to read the fault codes with a diagnostic tool.
4. A hissing noise when you park
A soft hiss near a wheel or the valve block, especially just after stopping, gives away a leak. Air springs usually crack where the rubber bellows folds.
5. The car does not rise, or takes a long time
If the car needs several minutes to reach its normal height after starting, or never gets there, the compressor may be weak, the relay may be faulty, the dryer may be saturated or the leak may be larger than the compressor can make up for.
6. Bouncing, knocking or less comfort
In an air strut, the shock absorber sits inside the same unit. When it wears out, the car bounces more over bumps, you hear dull knocks or the body rolls in corners, even though the ride height is correct.
7. The car leans or changes height while driving
If the car sits crooked with a full air supply, or rises and falls by itself on the move, check the ride height sensors and their linkage rods to the arms, which can bend or come loose.
How to find the source of the fault
- Read the fault codes. A diagnosis tells you whether the problem is height, filling time, a sensor or electrical.
- Inspect the air springs. Look for cracks, cuts or dry rubber, especially in the folds.
- Do the soapy water test. With the system pressurised, spray soapy water on the air springs, fittings, lines and valve block: bubbles show where the leak is.
- Check the compressor relay and fuse. A relay that sticks closed makes the compressor run non-stop and burns it out; one that does not close stops it from starting.
- Check the dryer and intake filter. A saturated dryer lets moisture into the circuit, which ends up damaging the valves and the compressor.
- Check the ride height sensors and their rods before replacing expensive parts.
What to replace
- Air springs and air struts in axle pairs. When a part fails through wear, the one on the other side has the same age and mileage. Replacing both on the same axle keeps the car balanced, and many manufacturers recommend it.
- The relay together with the compressor. It is a cheap part, and a faulty relay can burn out the new compressor.
- Fix the leak first, then the compressor. If you fit a new compressor without fixing the leak, it will be overworked again.
In our air suspension catalogue you will find air struts, air springs, compressors and valve blocks from brands such as Arnott or Dunlop, listed with their original (OE) number so you get the right part. You can also filter by car, for example air suspension for the Mercedes-Benz E-Class or for the Audi A6.
How to choose the right part number
The same model can use different parts depending on the version: 4MATIC or quattro all-wheel drive, adaptive damping (ADS, EDC…), engine or AMG/RS versions. The safest approach is to start from the original (OE) number stamped on the part or from the vehicle identification number (VIN). On our Search by VIN page you can identify your car and, if in doubt, send us your VIN and we will confirm the part before you buy.
Frequently asked questions
Can I keep driving with faulty air suspension?
As long as the car keeps its height and there is no “reduce speed” warning, you can drive carefully to the workshop. If the car sits very low, the tyre can rub against the wheel arch and the compressor overheats trying to lift it, so do not leave it for long.
How long does an air spring last?
It depends on climate, use and mileage. They commonly start to cause problems after 8 to 10 years or beyond 100,000 km, as the rubber loses elasticity and cracks.
Is it better to convert to coil springs?
Conversion kits that replace the air system with coil springs exist, but you lose height adjustment and some comfort. In Spain, changing the type of suspension may count as a vehicle modification, so check with your MOT (ITV) station before doing it.