Mercedes-Benz W211 Airmatic: rear sinks overnight or in frost
Why does the W211 Airmatic rear sink overnight?
The most common cause is an air leak. The air spring may be cracked or its protective bellows aged, or the aluminium at the joint between the spring and the reservoir may have oxidised and perforated. One leaking spring can lower the whole rear.
How is a W211 air spring leak found?
Lift the car and spray the springs, hose connections and air lines with soapy water. The leak may be in a line or the manifold rather than the spring, so check those first. If the rear does not stay up after switching off, the leak is big.
Why does the W211 rear sink in frost?
Often the compressor's dryer (silica gel) has become damp. The moisture freezes and the valves can be left slightly open. The drying granules and the air filter should be serviced; the interval is about 2-3 years. A clear drop still often points to a leak.
What other than the air spring can suddenly lower the W211 rear?
The rear axle level control rod or the level sensor arm can come loose or break, in which case the system thinks the rear is up and lets the air out of the springs. Air suspension is pressurised and affects driving safety, so leave opening the lines and replacing air springs to a workshop.