Power Sliding Door

I have a power opening sliding door that works via the switch on the dash.It only opens and closes sometimes after I have been driving for a while.Does anyone know how the motor operates(hydraulic or electric) I have a feeling it is hydraulic but cannot find anywhere to check the level.I have done a search on this site but can't seem to find anything.

Electric as far as I know. Clean the door contacts.

Hi Clive.Thanks for the reply.I have cleaned the contacts but it still does the same thing.I thought that it may be hydraulic because it will work after driving for a while and maybe the pressure may build.Maybe I might have to start stripping the area the motor is in and try and trace the source.