Garmin G3X Installation Manual page 473

If the test fails, the installation should be considered unreliable until the source of magnetic interference is
identified and remedied. The magnetometer interference test must be repeated until passed. When the
magnetometer interference test fails, record the three magnetometer maximum deviation values and their
corresponding timestamps. A maximum deviation value greater than 100% of the total limit in any axis
indicates a problem that must be resolved. Compare the corresponding timestamps with the prepared test
sequence to identify which action produced the problem. Contact Garmin for assistance in resolving the
problem.
NOTE
Two common reasons for a failed magnetometer interference test are:
1) New equipment is installed in close proximity to the GMU 22 magnetometer.
2) An existing or new electronic device has become grounded through the aircraft
structure instead of via the proper ground wire in a twisted shielded pair.
190-01115-01 G3X/G3X Touch Installation Manual - GDU 37X Config and Post Install Checkout
Rev. AA Page 31-21