DICE has announced that the vehicle disable from Battlefield 3 is being replaced by the critical hit system in Battlefield 4. In BF3, vehicles would become disabled after receiving enough damage. They would then require an engineer to repair it or the rest of its health would slowly bleed until destruction. As a result, 9/10 times players would bail the vehicle if no engineer was present.
In BF4 this system has been replaced or you could say modified. Now if enough damage is received in one hit, the game will decide to give it a Critical Hit or not. A critical hit will temporarily disable the vehicle like in BF3 but it can then be used again without the need of an engineer.