2002 ponatic firebird engine fault code P0440

have 2002 ponatic firebird with a engine fault code p0440 ( evaporative emission control system malfunction)
any idle what might be at fault, this is a v6 engine
DTC P0440: EVAP SYSTEM - LARGE LEAK
Description
The control module tests the Evaporative (EVAP) emission system for a large leak.
The control module monitors the Fuel Tank Pressure (FTP) sensor signal to determine the EVAP system vacuum level.
When the conditions for running are met, the control module commands the EVAP canister purge valve OPEN and the EVAP vent valve CLOSED.
This allows engine vacuum to enter the EVAP system. At a calibrated time, or vacuum level, the control module commands the EVAP canister purge valve closed, sealing the system, and monitors the FTP sensor input in order to determine the EVAP system vacuum level.
If the system is unable to achieve the calibrated vacuum level, or the vacuum level decreases too rapidly, this DTC sets.
Indy
 

Indy Shop owner By any chance was the vehicle running when the car was being fueled? Common mistake people make. Will cause the light to come on. Also the cheapest thing to do first is to replace the gas cap or lubricate the sealing O ring on the old cap. Then erase the code and see how soon or if it returns.