In the story Thomas Comes to Breakfast, from Branch Line Engines by the Rev. W Awdry, Thomas's driver tells him:
"You know just where to stop, Thomas! You could almost manage without me!"
Thomas, conceited, thinks this is literally true and that he does not need his driver anymore. So he decides to surprise the other engines by coming out of his shed by himself.
However according to the narrator:
Thomas thought he was being clever, but really he was only moving because a careless cleaner had meddled with his controls.
He is unable to stop, and crashes through the the buffers in a siding and into the stationmaster's house.
It seems that Thomas thinks that at least some of the actions he can take as a steam locomotive are caused directly by his own volition, but in fact they are caused by outside forces that he is unaware of. It appears that he is mistaken about, or at least overestimates, the degree of free will that he thinks he has.
However the Fat Controller and other railway staff certainly do treat him as if he is capable of forming intentions of his own, since they hold him morally accountable: "You're a very naughty engine, you will stay in the shed until you are wanted" etc.
Does Thomas the Tank Engine in fact have free will or not?
By free will, I mean the ability to form intentions which cause events to happen in the world, which would not otherwise happen.