It’s part of the evaporative emissions system (commonly referred to as “EVAP”) and reads pressure in the fuel system to detect evaporative leaks, such as a loose or faulty gas cap.

“Overfilling the gas tank can ruin the car’s evaporative emission control system. The EVAP system prevents gasoline fumes from escaping from the tank and fuel lines into the atmosphere.

P1456 - EVAP Control System Leakage (EVAP Fuel Tank System) If your engine light illuminates and your car fails an emissions ...