Mercedes-Benz W212 air suspension sinks overnight
The W212 S212 rear sinks overnight, what is the most common cause?
Most often the cause is a leaking air spring, which leaks especially in the cold. If the rear drops clearly on one side only, the leaking spring is on that side. The leak can also be in a hose, a connector or the valve block.
Why does the rear sink in damp frosty weather or even when no leak is found?
The compressor's drying granules become saturated with moisture, and water can freeze or corrode the valves so that they do not close tightly. Then the rear sinks on both sides. Service the dryer granules and the air filter first, before replacing more expensive parts.
How is an air suspension leak located?
Lift the car and listen for hissing; a small leak may not be audible. The folds of the air springs, the hoses and the connectors can be checked with soapy water. The air hose may be cracked or chafed near the compressor's protective cover.
Do both air springs have to be replaced and what else should be checked?
After one spring has been replaced, the other has often started to leak soon after, so it is worth replacing both at once. Also check the compressor fuse and relay and the joints of the height sensors; a seizing joint can give wrong height information. Air suspension is pressurised and affects driving safety, so leave opening the lines and replacing air springs to a workshop.