If you have a MK2 Nav System (female voice), you can bring up a Service Mode Menu as following:

• Set ignition to pos. II
• go to "settings"
• push the MENU button for at least 20 seconds
• The service menu has some TV options, GPS Data and telematik. Unfortunately, I only have an MK1 system, so I cannot tell you exactly, what youcan do with these options.