Nissan Repair: electric front motor mount, vehicle speed sensor, silicone fluid

Question
I have a 1999 nissan maximum that has a front engine motor mount What activates this and how dose it work. What procedure should I take in diagnosing this. This is the first one I have run in to

Answer
Patrick,

The motor mount is electric in that it, the motor mount, is hollow and is filled with ferro-fluid.  The fluid looks like black ink.  Actually, it is silicone fluid with iron ferrite, metal powder inside it.  Kind of like a creme filled donut.  The mount is soft at idle and in park.  This allows the engine to move around without the dash and steering wheel from shaking.  When the car starts to move the mount gets hard.  That is, an electro magnet is activated making the ferro-fluid get hard.  The result is the mount stiffens up and the car has crisp handling.  Stop and it gets soft again.  There is a relay that activates the mount.  The computer grounds the mount by information from the vehicle speed sensor.  No square wave generates and no gounding of the circuit that powers the mount.  I have had to change several of these mounts due to leakage.  If you get what looks like dirty oil on the ground and trace it to the motor mount you have found a mount that needs to be replaced.  If you wanted to diagnose the mount and are unsure if it has leaked.  Really, you will know from the black goo.  Anyway, provide power to the circuit and you will actually see the mount stiffen up.  Get the car on a lift or jack stands and check it out.  Email me back if you need more.