Small Leak Test
WARNING: This page is about a different car, the 2004 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
If the large leak test passes the PCM will continue to monitor the fuel tank pressure (FTP) sensor signal in order to determine if there is vacuum decay. A slight increase or rise in pressure indicates there is a small leak in the evaporative emission system. The EVAP control system is required to detect evaporative emission fuel system leaks as small as 0.5 millimeter (0.020 inch) between the fuel fill cap and the purge valve. If the PCM detects vacuum decay was evident for two consecutive trips, the MIL will be illuminated, and a DTC P0456 will set.