Who told you that if there’s air in the system “it” will shut down the pump? The pump is drawing from the bottom of the tank and should have a uninterrupted supply of water. If you have one of the center tanks that lay flat in the trunk, then you need to keep the fluid level high enough so as to not uncover the pump when braking. If you run less than 5 gallons then that could happen. That’s why the stand-up/side-mount is better. As long as the pump is supplied with sufficient water it will simply push any air in the system through and it will end up back in the tank through the return line. If the pump is not running then it’s either the electrical to the pump or the pump itself.