Maximum Overdrive

"Maximum overdrive" is a phrase said by Optimus Prime when he wishes to start driving faster than his normal speed.

"Darkness Rising, Part 2"

 * When running over Vehicons and drilling machines in the Nebraskan Energon mine.

"Darkness Rising, Part 5"

 * When GroundBridging to the space bridge.

"Convoy"

 * When pursuing a derailing train carrying a nuclear device. This time it was shown to be an activation code for his truck mode to rocket past and stop it.