964 C4 awd grinding

[leftfootbrake]

Hey guys so I got a c4 about a year and a half ago. has about 90k miles.

Recently the awd system warning siren alarms and if the car is driven any turn from center makes a grinding sound.

People have said to add fluid and its topped off

Any suggestions?

[993Speedster]

The warning lights sound like one thing... but the grinding when making a turn sounds a whole lot like center diff/planetary gear failure. I think Porsche might call it a sun gear if it ends up being the case.

Put the car up in the air in neutral and spin 1 or both of the rear tires. If you spin just 1 (left or right) rear tire, you should be able to make all 4 rotate as there is a little bit of drag on the rear diff and center diff clutch packs. Now rotate the rear tires in opposite directions, you should feel a little tiny bit of resistance but still be able to make them go different directions. Also note if you get any rumbling/feedback in rear diff as you make them rotate different directions. Should be a smooth-ish slip.

Now put vehicle in 1st gear/park and try and rotate rear tires (both forward) and see what happens. With car in park/1st gear and rears rotating forward, you're moving the center diff/planetary the fronts should be rotating the opposite way now and you might/should feel a tiny bit of clutch pack drag (depending on age and wear at this point really) in the center diff. If you get a whole bunch of feedback and noise coming from the nose-cone of the transmission when doing this last bit or you cannot rotate them different directions (ie front and rear locked together full-time)... NOT good