DTC P0442 Or DTC P0455: Condition

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

With engine running, ECM (PCM) closes EVAP canister air valve and opens EVAP canister purge valve. If EVAP control system is okay, EVAP control system pressure detected by fuel pressure sensor is lowered. When EVAP control system pressure is lowered, ECM (PCM) closes EVAP canister purge valve, leaving EVAP canister air valve closed. If EVAP system is okay, fuel tank pressure will increase to a predetermined level.

DTC P0442 is set when fuel tank pressure increase exceeds a predetermined value. MIL is illuminated when ECM (PCM) detects malfunction during 2 consecutive drive cycles. DTC P0455 is set when fuel tank pressure change is less than predetermined. MIL is illuminated when ECM (PCM) detects malfunction during first drive cycle. Possible causes are:

Missing, loose or malfunctioning fuel filler cap.
Loose or plugged vacuum hose.
Components mounted to fuel tank leaking in area of mounting.
EVAP canister plugged.
EVAP canister purge valve malfunction.
EVAP canister air valve malfunction.
Fuel tank pressure control valve malfunction.
Fuel Tank Pressure (FTP) sensor malfunction.
Fuel level sensor malfunction.
ECM (PCM) malfunction.