I have a GE glass top drop in electric cook top (JP655) in my kitchen. Over the past week I have noticed that one of the burners is med-high to high regardless of what the knob is set at. Does anyone know of a potential cause or fix? I hope to not have to replace the whole unit.
The surface element controller has probably failed. Replace it. Personally I would use only a genuine GE part, but you may be able to get a genuine GE part cheaper than from GE. But if you already have a non-GE part on order you may as well try it. These parts cannot be easily tested with a meter by a DIYer. One just puts it in the range and sees if it works.
Note that your range will have different controllers for different sized burners, at least that is the case for mine.