Sounds normal. It extends till it stops. When the motor runs without the step moving, it increases amperage draw which the sensor senses. When it senses increased amperage draw, it shuts off. That is not an instantaneous happening.
If it clicks when retracting And when it extends High probably of broken teeth on the main gear in the gear box, And you will need to buy a new gear box for your step, it will work as is until too many of the teeth break, which could leave you in a situation where the step does not retract all the way and keeps clicking until you will power
Which Brand step do you have? If Kwikee---BAD MOTOR. If LCI(Coachstep) it is either the pie shaped drive gear(missing teeth which you can see) or a bad motor. PS, either brand should NEVER click. Doug