You need to switch from NAV to GPS mode.

Many of us have added a NAV/GPS Switch to the 2D Autopilot panel. Some have also created a keyboard command to the NAV/GPS Switch (I use CTRL+SHIFT+N).

This is how my 2D A/P Panel has been changed to add the (Cessna) NAV/GPS Switch:

[Window03]
Background_color=0,0,0
size_mm=457,106
position=2
visible=0
ident=10005

gauge00=Captain_Sim.p721.P12!P12_001_ap,  30,0,427,106
gauge01=Cessna!Nav GPS Switch,  0,0,30,30
gauge02=Cessna!Nav_GPS_Annunciator,  0,30,30

You have to change the size_mm to be able to see the switches and the A/P and add the two NAV/GPS Switch.

Mark