I'm going to forward you everything I have on this concern.
The hyundai accent GS 1.6L has a DM-TL Diagnistic Module for Tank Leakage Module.
DTC P1401 Diagnostic Module-Tank Leakage: System malfunction
This is not a Evap Leak Code, it is a component malfunction code.
CANISTER For evaporation monitoring, there are a DM-TL (Diagnosis Module for Tank-Leakage), and an air filter as the illustration.
Look for distortion, cracks or fuel leakage.
After removing the EVAP Canister, inspect for cracks or damage.
Diagnosis Module For Tank Leakage (DM-TL)
PRINCIPLE OF OPERATION The diagnosis module comprises an electromechanically driven 1-overpressure pump together with a 2-change-over valve with integrated 3-reference restriction. In the change-over valve's setting "a" as shown, the pump delivers through the reference restriction. In the other setting the pump delivers through the 4-canister into the fuel-tank system. The engine-management system measures the pump's electrical current consumption in each setting. A comparison of the currents is a measure for the leakage in the tank. If the electrical current consumption is identical in both settings, this means that there is a tank-system leak which is equal to the reference restriction. In order to make the procedure independent of environmental influences and tolerances in the overpressure pump, the system performs a comparison with a reference restriction. Outside of the leakage-diagnosis mode, the change-over valve remains in the "a" setting. The canister can be regenerated via a large flow cross-section, and only an insignificant pressure loss occurs. This is advantageous above all on vehicles with high canister-regeneration rates.
This is absolutely everything My database has to offer on this code.
I would check the Fuel Tank Cap Seal and be sure the Cap is Sealing correctly,
Be sure to have the trouble code cleared,
I hope this is the information you are looking for.