Transformation paralysis

Transformation paralysis (also known as mode lock) is a condition where a Transformer finds themselves locked into their alternate mode.

The Transformers cartoon
In 1985, when the Autobots participated in a race for charity, Megatron took the opportunity to test his latest creation, the Transfixatron, a weapon which locked a Transformer in whatever mode they were currently occupying. When Starscream dissed the device and Megatron's leadership, he was locked into fighter mode and had to beg his leader for mercy. With a successful demonstration under their belts, the Decepticons used the Transfixatron on the majority of the Autobots while they were stuck in vehicle form and captured them. While Megatron attempted to destroy the Autobots via an overly-elaborate trash compactor, Ratchet and Wheeljack create a device that would reverse the effect... a grenade. With the Autobots back to normal, they forced the Decepticons into retreat by firing the Transfixatron at Devastator, though instead of locking the Constructicons in that form, it for some reason forced them to separate.