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Garmin GNC 255A/255B Pilot’s Guide
190-01182-01 Rev. A
Problem Possible Cause Action
GNC 255 does not power on No power to the
GNC 255
Check power connections,
breakers, and main
avionics switch
Faulty electrical
wiring or connection
Contact your dealer to
perform electrical system
test
No Nav audio Output disabled or
set to a low level
Contact dealer
Nav audio in Com Mixed with Com
feature
Contact dealer
GNC 255 does not transmit No power to Com Check power connections
Mic key connection Check Mic key input
connection
Intercom doesn’t function It can be enabled
or disabled via a
remote mounted
switch or via the
menu.
Check connections
No voice activation,
or if must talk too
loud
Check ICS page, Intercom
On/Off, Adjust Intercom
Can’t change active frequency Com Radio not
communicating. The
radio may also be in
lockout mode. In this
case the radio would
be tuned to 121.50
and the active freq
would not be able to
be changed.
If in Lock Out mode,
press the external Com
FLIP/FLOP key for two
seconds to return to
normal operation or cycle
the avionics power. If the
condition persists, contact
dealer.
OBS readout displays “---” Resolver failure Contact dealer
Calibration error Recalibrate resolver