I'll save Dave some typing and answer this :
It is the evap purge solenoid.
The PTCM commands it to open the vacuum line to the fuel system upon engine startup to create a slight vacuum in the system.
The PTCM then monitors to see how long it takes for the system to return to ambient pressure.
If that time is shorter than it expects, then it decides that there must be a leak somewhere and flashes that light and sets that P code just to ruin your day.
( not too sure about it flashing the indicator, but I do know it sets the P code )

It is not a catastrophic condition, other than the EPA may arrest you for over polluting and lock you up for life + 100 years.