Mercedes-Benz W220 sagging overnight: finding the Airmatic air leak
Mercedes-Benz W220 sinks overnight, where does the air usually escape?
The most common leak points are the top end or air bag of the air spring (strut), the valve block and the compressor's pressure relief valve. If only one corner sinks, the fault is usually in that corner's air spring or its air line.
How do I find an Airmatic leak on a W220?
Hose connections and the tops of the springs can be checked with soapy water: bubbles rise at the leak. An internal leak in the valve block is tested by disconnecting the hose between the block and the compressor and putting its end in a glass of water. No bubbles should come out at all.
What fixes the sinking on a W220?
An internally leaking valve block is replaced. For a leaking air spring top end, a repair kit with a cover O-ring is available, or the spring is replaced. The compressor's air dryer can be damp, and water can jam the valves, especially in freezing weather.
Is the compressor hiss after switching off a fault?
No. The hiss of the pressure relief valve after switching off is normal and shows that the valve works. It is a fault only if the car still sinks overnight. Air suspension is pressurised and affects driving safety, so leave opening the lines and replacing air springs to a workshop.