Originally Posted by Types4
Neutral and reverse have a switch. 1-6 doesn't have anything at all. The ecu calculates takes into account the vehicle speed and rpm once you get off the clutch, and figures out what gear it is in.
That, and there is a clutch position sensor. It will only read out when the clutch is all the way up. If you have a faulty return spring, you will not get anything on the display, and the car will think it's still in neutral.
(Source - My faulty clutch return spring)