You probably have a wiring problem between the sensor and the timer. You need to take off the front and trace the wiriting from the sensor to the timer and check it for a bad connection and for continuity.

If the problem is in your timer I would go to timed drying rather than spend the money for a timer and not have the problem fixed, but if you cannot find the problem in the wiring you can certainly try that option if you really wanted to use that cycle.

Good luck and please post what you find.