2002 BMW 745Li Active Suspension System Air Compressor Replacement Cost

Active suspension systems come in a few forms, the most common of which are air suspension and hydraulic suspension systems. Air suspension, otherwise known as air spring suspension or pneumatic suspension, use a compressor to pump high pressure air to the air springs to inflate them when needed. High pressure is always maintained in the system so the air springs can adjust at will, and the compressor will run any time it is needed to replenish this pressure.

The air compressor for pneumatic active suspension systems functions by high amperage switched power, which is turned on and off by a control module or relay. Any time the height sensors, pressure sensors, control module, or suspension mode selector switch request an increase of pressurized air, the compressor is activated, and pumps that pressurized air to the springs where it is needed.

Air compressor failure is evident in that the entire system will either cease to function, or the compressor will constantly run with or without achieving its target pressure in the system. This can happen even when the vehicle is off, and battery drain may occur until there is insufficient power to activate the air compressor relay. In nearly all cases, all four corners of the vehicle will sag to the extent that the vehicle ride height is much lower than desired. Also, the ride will be extremely uncomfortable. In some cases, the suspension may not sag for quite some time, but ride quality will diminish as will the ability to adjust the suspension with the mode selector. Finally, a hissing may be heard from the compressor in the event of an air leak from the compressor or manifold.