It is an electrically locked rear differential thats locks both rear wheels together giving power to both rear wheels instead of one as in most Tacomas. Unless you have the TRD Offroad package you probably have a standard differential. If its a locker there would be a push button switch on your dash to the left of the steering wheel and next to the clutch cancel switch. I still cant figure why they called it a center differential when its the rear. Did they call you with an estimate first? You could have gotten a used third member "rear differential gears" from a junkyard for alot less.