I had the same problem.
It ended up being a "bad" motor. I replaced the motor and mine is working fine now.
The motor would raise the spoiler up 1", bind up and stop.
No problems lowering the spoiler at all.
I am not sure if there is a limit switch (I doubt) or it just runs till a certain amount of resistance is met and stops.
You could also try cleaning and lubing the spoiler cylinders (or whatever they are called) that the spoiler rides on and see if that helps.
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