If your vehicle is showing gas pump nozzle keeps clicking off constantly when trying to fill the tank, here are the most likely causes and the parts you'll need to fix each one.
The vent valve opens to allow air and fuel vapors to escape the gas tank while you fill it. If it gets stuck closed or clogged with dirt and debris, the trapped air pushes fuel back up the filler neck, triggering the pump to shut off.
The charcoal canister absorbs fuel vapors. If you have a habit of 'topping off' the gas tank after the pump clicks, liquid fuel can flood and ruin the charcoal inside, completely blocking the airflow needed to fill the tank.
The hose or vent tube connecting the gas cap area to the tank can become kinked, pinched, or internally collapsed. This is highly common if the fuel tank was recently removed to replace a fuel pump.
On certain vehicles, a leak detection pump tests the emissions system and also acts as the primary vent path. If this pump fails in the closed position, it will prevent air from escaping the tank during refueling.
A safety valve built into the top of the gas tank prevents fuel from spilling in the event of a rollover. If this mechanical valve gets stuck closed, it blocks the tank from venting. This usually requires replacing the entire fuel tank.