I'd start by lubricating all moving joints (usually more than 20 points) and see if that works. Use something other than WD-40, a spray white lithium grease lasts for a while. The motor and gear mechanism is the same as an electric window motor and gear. The control board shuts off the motor when a high current draw is detected. If you determine it is the motor, take it off and go to an auto parts store for a replacement -- much cheaper than buying from the step manufacturer. Be careful around the step, they can suddenly move and pinch or bite you!
Kwikee by Lippert makes many of the steps used in RVs, look up your manufacturer and you'll find manuals online.
There are many threads about step maintenance, use the search box at the top right of the page with the Google logo.