just continue on with the main quest and you'll be able to do it.
It is a quest added after finding dad or Docter Li.
id say about half way through the main quest.
All you need is to get into the chamber with the purifier and type in the code 2:16 (the waters of life) The code the character's dad told you was your mother's favorite verse
You must first complete a quest called "The Waters of Life". First you have to track down James, the player character's father, and the story progresses from there.
you have to complete the quest (The Waters of Life) to get access to the Citadel. http://fallout.wikia.com/wiki/Portal:Fallout_3
You will not get in until you finish Waters of Life quest, at the very end of the quest you escort Dr Li through Taft Tunnel and she then leads you into the Citadel. Once you have entered your free to come and go as you please.
He is in the citadel. You will reach it after the waters of life quest. After the Cutscene with li and lyons talk to lyons about power armor training. Gunny will be in the courtyard during the day.
Yes, it is possible to gain access back into Vault 101 on Fallout 3 for Xbox 360. In fact sometime after you escape there is an optional quest where Amada needs your help because "chaos" is happening.
do the quest agethas song to get the location and passwords for all vaults (exept 101 cos anita changed the password for the quest trouble in the homefront you get this after the waters of life quest just walk neer top 101 and youl pick up the vault 101 emegency brodcast from anita asking you to help her)
Do the main mission the waters of life then docter li will talk on an intercom outside of the citadal then the brotherhood of steel will let u in
If you begin walking without turning around they might follow.If the don't move try to fast travel to the citadel. If there not, then maybe the quest isn't active or your game is glitched. Try to find a patch regarding your problem depending on what consol you have.
pip boy from fallout 3 made life and the universe