Dryers with electronic control and auto dry cycle indeed use moisture sensors for the auto drying to work. The problem is absolutely associated with the failure of the moisture sensors, especially when the timed dry cycle works fine. Either the connection of the sensors to the electronic control is loose or the sensors are covered with thin film that prevents it to sense the proper moisture content of the clothes.

Clean the moisture sensor bars thoroughly and make sure its connections are snug fit. Reseat the connections several times to clean off dirt and corrosion build up in the connectors and terminals. The last thing to look into is the electronic control if all resort fail to address the issue, that is, clean sensor bars and good terminal connections.

Indicate the exact model number of the dryer should you need further or more specific troubleshooting and repair advice.