Conditions For Setting DTC
WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
DTC P0455 will set if the FTP cannot be pulled greater than 2.02 volts, -2.61 in. H2O (-4.88 mm Hg) during the EVAP diagnostic system test indicating a large EVAP leak.