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:

Blockages or kinks in EVAP canister tube or EVAP canister purge outlet tube (between fuel tank, EVAP canister purge valve and EVAP canister).
Fuel filler cap stuck closed (no vacuum relief).
Contaminated fuel vapor elbow on EVAP canister.
Restricted EVAP canister.
Canister Vent (CV) solenoid stuck open (partially or fully).
Plugged CV solenoid filter.
EVAP canister purge valve stuck open.
VREF circuit open (harness near FTP sensor, FTP sensor or PCM).
Damaged FTP sensor.