Trouble code P0440 is a malfunction of the Evaporative Emission Control System for the GM line of vehicles, states OBD-Codes.com. The parts possibly responsible for the code are the gas cap, purge solenoid or canister.
Onboard Diagnostic System codes notify the driver that the car systems are experiencing a malfunction of some part of the vehicle emissions and need to be checked. Codes are comprised of alphanumeric values as assigned by the Society of Automotive Engineers.
The OBD II system tests the emission systems either periodically or continuously. The “Check Engine” light activates when one or more of the diagnostic tests is an outlier or the system fails the test. Usually, the light remains on while the issue exists, but it may clear itself when the readings fall within normal range, states Trouble Codes.
The EVAP keeps gas fumes in the fuel system. Hoses carry the vapors through the system to the charcoal canister. The vapors are held in the canister until the engine is turned on and the vapors are siphoned into the engine through the purge control valve opening.
Diagnose the issue with the GM vehicle by checking the integrity of the hoses and other parts of the EVAP. This includes the gas cap, hoses and tubes. If no holes or cracks are identified, a professional uses a smoke machine to double check the system for leaks, according to OBD-Codes.com.