Garmin G1000 Reference Manual page 159

APPENDIX A
System Annunciation Comment
Display system is not receiving vertical speed input from the air data com-
puter.
Display system is not receiving valid heading input from the AHRS.
The GPS information is either not present or is invalid for navigation.
Note that the AHRS utilizes GPS inputs during normal operation. AHRS
operation may be degraded if GPS signals are not present (see AFMS).
Display system is not receiving valid transponder information.
A red 'X' through any other display field (such as the engine instrumentation
Other Various Red X Indications
fields) indicates that the field is not receiving valid data.
Garmin G1000 Cockpit Reference Guide for Cessna Nav III 143