Possible Causes

WARNING: This page is about a different car, the 2002 Mazda B4000, 2002 Mazda B3000, and 2002 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.

Possible causes are:

Aftermarket EVAP hardware (i.e. fuel filler cap) not meeting required specifications.
Small holes in fuel vapor hoses/tubes.
Canister vent solenoid stays partially open on closed command.
Damaged, cross-threaded or loosely installed fuel filler cap.
Loose fuel vapor hose/tube connections to EVAP system components.
EVAP system component seals leaking such as EVAP canister purge valve, fuel tank pressure sensor, canister vent solenoid, fuel vapor control check valve tube assembly or fuel vapor vent valve assembly.