You won't find anything interesting at the parking, only few radroaches. You should rather focus on what can be found in the nearby stash in the western corner of this part of the map. There you will find entrance to the water pumping station.
Inside there is a lock to open which you need password. The password can be found on the pillar behind you - 10, 4, 5, 1. You must press the buttons on the machine at the door in order to display the password from left to right. Each time you press a button the counter is increased by 1. Behind the closed door you will find a chest with ammunition and unique The Gainer weapon.