Repair stations
Repair stations might be scatter around the map if your vehicle it's damage or out of ammo, you can bring it to one of these repair stations where the vehicle will me immediately refill it's ammo and slowly be repaired when standing still. (Notice: this only works for land vehicles, airplanes have a completely different repair station usually situated in the sky)
Repair kits
All tank crews and enginnears have at their disposal repair kits, repair kits are often used when a vehicle it's still operative but their tracks and/or wheels have been destroyed, in that chase someone has to use a repair kit on the damage vehicle for it to be allowed to move again.