The EVAP system (Evaporative Emission Control System) avoids gasoline vapors going out into the atmosphere from the fuel tank or fuel system. This system eliminates fuel vapors because they pollute the atmosphere.
To achieve this, the vent lines from the fuel tank and carburetor bowl direct the vapors to the EVAP storage vessel. The vapors are trapped in the EVAP storage canister until the engine is started. After the vehicle is being driven, the Powertrain Control Module (PCM) opens a bleed valve to allow the vapors to be diverted to the intake manifold storage canister so they can be burned in the engine.
The EVAP system is monitored by the PCM through a pump, which detects possible leaks in the system, which is activated once the engine is turned off. If the DTC P2401 OBD2 code is set, it is because the PCM found that the injection pump circuit of the EVAP system has a low voltage.