Not really sure what you are saying.First of all what model is it XE,XS or XT. When you say it kicks in does the light come up on the dash showing it engaged

 

Hi its a Sorento XS. no the light doesnt come on the car just starts juddering and whining. if I stop/slow down flick the 4x4 switch to on and off it disengages itself but as soon as I go round antoher corner it locks in again. my mechanic is looking for a replacement dif to see if that fixes it. the diff itself seeems ok but when its connected to thecar it starts locking up???

 

So are you saying it is not the 4WD kicking in.The model you have has the TOD system.First step in fault finding you MUST have the best tyres on the rear.Then if it still does it remove temporarily just for testing ,the fuse in drivers footwell marked TCCS .This will throw lights up on dash but ignore whilst testing.If problem goes the fault lies with the transfer box not the diff.

 

thank you will pass on to my mechanic....

 

Do you know if the rear diff locks by itself?

 

The rear diff is the main diff which drives the motor.The front diff only engages if the rear wheels are loosing grip.This is actuated by the speed sensors to the front and the rear.If the rear tyres are worn more than the front the sensors will b telling the control unit they are slipping.If only fitting two new tyres and not a full set they must always be fitted to the rear.Some Sorentos had a limited slip diff,but others did not.With the rear wheels off the ground if one wheel is turned the other should turn in the opposite direction.If limited diff they will both turn the same.If the rear wheels are off the ground and the front ones still on the ground you should be able to rotate the rears.If not this means the rears are still connected via the transfer box to the front.This will point to transfer box problem as the clutch inside should not be engaged.