2000 Chevy Blazer Car Trouble

The possible causes of a code P0440 could mean one or more of the following :
1. The gas cap is not installed or working properly.
2. The purge solenoid has failed.
3. The canister is plugged and not working properly.

1. Remove and reinstall the gas cap, clear the code, and drive for a day and see if the codes come back.
2. Inspect the EVAP system for cuts/holes in tubes/hoses.
3. Inspect for damaged or disconnected hoses around the Evap purge solenoid.
4. Inspect and/or replace the sensor.
5. Inspect and/or replace the purge valve.
*I recommend you have a professional use a smoke machine to detect leaks.