I Think My Rav4 Has A 3rd Diff Problem, Can Anyone Enlighten Me.

[RavenRob]

Hi My drive is a 1995 Rav4 L Auto. I will give a bit of history that may be the cause of the problem. 6 mths ago I put new tyres on the front two wheels, as the rears still had a few thousand kilometres left in them I made the decision to leave them till the next warrant of fitness in 6 months time. On the 5th month a warning light started flashing, it was the O/D off light. After reading your forum I found how to read the code which told me that there was a speed differential between the front driveshaft and the rear one. I thought, problem solved, put the new tyres on the back and cancel the warning and all will be good. Didn't work, After driving 1 kilometre, the warning light came back on and I have a suspicion that the 3rd diff is stuck in difflock. The car appears to drive OK and there are no serious noises coming from anywhere except when I do a slow tight 'U' turn on gravel I can hear one of the back wheels skid on the loose gravel. Any answers out there please? or how i can do other tests to check if the 3rd diff is locked or not.