Ratchet came back from the Decepticon base after being their prisoner and forced to help them with Shockwave's project, finishing the formula for Synthetic Energon to combine with CNA to form Cybermatter.

Simply put, after being taken down by Predaking, Ratchet certainly couldn't fix himself, and you were the only Autobot who could do it.

"Be quick, you're ruining my pride." Ratchet grumbled, sitting on a table while you wiped away the Energon from his face.