Air suspension problems: the signs, the causes and the repair

Air suspension gives large cars their ride: a Range Rover, a Mercedes-Benz S-Class or GLS, a Porsche Cayenne, an Audi Q7, a Bentley. It also has more parts than steel springs, and in the heat those parts age faster.

How the system works

Each corner has an air spring, a rubber bellows that holds the car up. A compressor fills the springs through a valve block, a small tank keeps a reserve, and height sensors tell the control unit how the car sits. When everything is tight, the compressor runs for a few seconds now and then.

The signs

• The car sits low after a night parked, at one corner or one end. Air is escaping while it stands.
• The compressor runs often or for a long time. It is making up for a leak.
• A suspension warning, sometimes with the car locked at a low height or its speed limited.
• The car leans, or rises unevenly when it starts.
• A harsher ride than the car used to have.

The usual causes

• A leaking air spring. The rubber cracks where it folds, and heat and sand speed that up. It is the most common fault on a car more than a few years old.
• The valve block or an air line, which lets the pressure out slowly.
• A tired compressor. It is rarely the first thing to fail: it wears out because a leak kept it working.
• A height sensor or its linkage, which gives a false reading.

Why a small leak should not wait

A leak makes the compressor run longer and hotter, and a compressor that overheats fails. One air spring replaced early is one repair. The same leak left for months often adds a compressor, and sometimes a relay and a drier, to the bill.

How the fault is found

The fault codes show which corner or component the control unit distrusts. Then the system is tested: ride heights are measured, the springs and lines are checked for leaks, and the compressor’s output is compared with what it should deliver. Replacing parts by guesswork is expensive on air suspension, so the test comes first.

Is it safe to drive?

A car that has sunk is riding on its bump stops, with little suspension travel and poor steering response. Drive gently, keep the speed down and have it looked at soon. If the warning is red, or the car is clearly on the ground at one corner, do not drive on.

In the UAE

Summer heat is hard on the rubber of the air springs and on the compressor, which sits where it gets little cooling air. Speed bumps and steep car-park ramps keep the system working all day. A check of the ride heights and of the compressor’s running time at each service catches most leaks before they strand the car.