How to test transmission speed sensor?

I have a 2002 Audi A4 1.8 Turbo Quattro with an automatic transmission.

  1. Would anyone know how to test the transmission speed sensor? How do I ensure that it is working? The Audi original part number is 012 409 191D.
  2. What voltage reading should I be getting from the transmission speed connector with the car on, but the engine not running?
    Any help would be appreciated,
    Thank you.