Q: Convertible top sometimes works

The Audi A4 conertible top system monitors a total of 10 microswitches and 1 sensor to determine the soft top position and position of the trucklid and cover. What is likely happening is that the status of one of these microswitches is giving an incorrect or implausible position. Likely candidates are the the microswitches in the locking motors at the cowl. The wiring bends with the top and can break causing intermittent contact and can possibly cause a bad signal. The wiring needs to be traced and see if a break can be located. A scan tool that can read the sensor statuses as the top operates may need to be used to determine where the problem arises. You may need to enlist the help of a mechanic, like one from YourMechanic, who will have the access to the wiring diagram and the expertise to diagnose the top issue.