When you arrive at Ilos in the Mass Effect Legendary Edition, Saren is ahead of the way to get to the pipeline. You arrive at the planet in Maku and he closes the door behind you and lets you fight Geth, who is left behind. If you want to break through the door, you’ll have to override security, but you don’t really have any direction where you need to go.
How to override security on Ilos
You will have to get through the Plaza of Ilos, to the courtyard. There will be a lift that will take you down to the security room. But until then, you’ll have to fight your way through a decent amount of Geth. While you can ignore this, if you don’t eliminate all the geth in the area, there will be a lower location. Clean the Plaza area, then walk through the courtyard to find the elevator.
When you go down to the next part, you enter the Armature Bay and above it is the Security Room. Again, there will be a lot of Geth in your one. There is also Geth Prime, which is one of the strongest enemies you can fight, so expect to fight some of the smaller enemies before you focus on Prime.
When you’re done with them, go to the back of the room and go up the ramp. There will be a security panel with which you can communicate, and you will be able to proceed towards the next area and go after Saren.