Open the Precursor door was a mission that Jak and Daxter completed to obtain a power cell in The Precursor Legacy. A continuation of the training course, introducing Jak to blue eco and the effect it has on some Precursor artifacts.
The PlayStation 3 and Vita versions of this mission are related to a trophy named "Open Sez Me", completing this mission will reward you with a bronze trophy.
After a little practice with the blue eco clusters, you will reach a plateau with a large Precursor door crafted out of Precursor metal. Samos will tell you that you need to be charged up with blue eco in order to open it. Simply collecting and channeling the clusters you ran into earlier will not do, as they will not be sufficient and last long enough to charge you up until you reach the door.
Walking onto a nearby bridge will trigger a cinematic with Keira detailing the use of eco vents. The blue eco from the vent will last long enough for you to simply walk back to the door before the effects wear off, when done so the blue eco activates the doorway causing it to open. The power cell is right behind it on the other side.