DTC P1450: EVAP Control System Malfunction (Excessive Vacuum): Condition

WARNING: This page is about a different car, the 2002 Mazda 626. However, it is still accessible from the selected car via links, so may be relevant.

DTC is set when Powertrain Control Module (PCM) detects fuel tank pressure is less than -3.91 in. Hg and following monitoring conditions are present. Intake air temperature is less than 102°F (38.9°C), fuel tank pressure is -.55-2.9 in. Hg, calculated load is 15-80 percent, vehicle speed is 25-75 MPH, fuel tank level is 15-85 percent, and atmospheric pressure is more than 22.5 in. Hg. This is a continuous monitor. MIL is illuminated when PCM detects malfunction during 2 consecutive drive cycles. Possible causes are:

Canister Drain Cut Valve (CDCV) malfunction.
Plugged canister vent side filter.
EVAP canister malfunction.
EVAP drain passage plugged.
Fuel Tank Pressure (FTP) sensor malfunction.
Purge solenoid valve malfunction.