Primus is Cybertron itself. The core of Cybertron is the centre of Primus' conscience, and so to contact him, you must be at the core. The only way to reach him is to go though the Omega Gate

War for CybertronEdit

Decepticon Chapter 5Edit

Once Omega Supreme opens the Omega Gate, Megatron infuses Dark Energon into Primus

Autobot Chapter 3Edit

Primus informs Optimus Prime that they Autobots must leave Cybertron, as he has to shut down completely so he can purge the Dark Energon from his systems. He then gives a portion of his spark to Optimus, and names it "The Matrix of Leadership"