DTC P0456: EVAP Control System Leak Detected, Very Small Leak: Condition

WARNING: This page is about a different car, the 2002 Mazda Protege5 and 2002 Mazda Protege. However, it is still accessible from the selected car via links, so may be relevant.

DTC is set when PCM detects fuel tank pressure reading that exceeds threshold values after Canister Drain Cut Valve (CDCV) is closed. This is monitored when following conditions are met:

Atmospheric pressure is more than 20.5 in. Hg.
Fuel remaining is 35-85 percent of total capacity.
Intake air temperature is 14-140°F (-10-60°C).
Engine coolant temperature is 95°F (35°C) or less when engine is first started.
Engine coolant temperature is 158-226°F (70-108°C).
Throttle opening angle is closed.
Within 16 minutes of engine start.

This is an intermittent monitor. MIL is illuminated when PCM detects malfunction during 2 consecutive drive cycles. Possible causes are:

CDCV malfunction.
Catch tank malfunction.
Charcoal canister malfunction.
Fuel pump unit poor seal.
Fuel tank malfunction.
Evaporative hoses damaged or loose.
Evaporative pipe damaged.
Loose, missing or defective fuel filler cap.
Purge solenoid valve malfunction.