Engine Mounts (4 mounts per vehicle)
1 Electronically Controlled Liquid Filled, 3 Static
Basically the solonid control valve is connect via the engine CPU to determine RPM etc. This determines if it should open or close the valve to allow the fluid on the front engine mount to flow back and forth from the main to the supplemental chamber. Thereby making this mount "Softer" or closed "Harder".
You only actually have to regulate the one in the front to effect the whole stems ability to allow more of less engine rock or said another way transmit force pulses into the vehicle structure.
Here is anothers description of a systme "similar" to ours:
Basically it's a hydraulic mount that has two chambers filled with fluid. A large orifice valve and a small orifice valve connect the chambers. The large orifice is a rotary valve while the small orifice is always open. The small orifice makes the mount work like a stiff shock absorber.
When the engine is idling, a vacuum motor turns the large orifice valve to the open position. This allows more fluid to move between the two chambers. This makes the mount softer and absorbs engine idle shake. The Powertrain Control Module (PCM) controls when vacuum is applied to the large orifice valve through a solenoid valve.
Above idle speed, vacuum to the large orifice valve is vented and closes. It goes back to the small orifice operation and becomes stiffer. To check it, apply vacuum to the engine mount with a hand vacuum pump and note the reading. It should remain steady. If it drops the engine mount is bad and needs replacing