Gm Engine Code Po449 & Po455

[thebigdad]

I purchased a new evap vent solenoid, ACDelco 19207763. I began installation by checking the electrical, with the key off one side had 12 volts, nothing on the other side (ground?). With the motor running my meter read 13.5 volts across the two terminals, also the ground side tested to have continuity with the engine running, all this is consistant with the information I have read, that there is power all the time and that the ECM connects the ground. My question is should the solenoid be closed when voltage and ground are present? There seems to be no restriction in blowing thru either the old or the new solenoid when disconnected from the electrical connection or when connected to the electrical with the engine on. When is the solenoid closed? The code PO455 refers to a large vaccum leak which I assume is consistant with the solenoid open. I want to make sure I fix the right thing. I have not installed the new solenoid. Could the new solenoid be defective?

Any advise will be greatly appreciated. Thank you