Porsche Cayenne 2009 Diesel

[o.nunn]

Hi

I'm having trouble with what I believe to be something to do with the dif as when I try and flick the switch in to the motorway mode..nothing happens.
Is the red light supposed to come on and is there supposed to be a four wheel drive symbol on the dashboard?

I get a serious vibrating at 40mph and cannot go any faster because of noise and vibration gets worst. Does anyone know what my problem might be.

So far I've changed the transfer box actuator but this has made no difference whatsoever.

Thank you