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No Attitude Data
If the error message "No Attitude Data" displays on a Garmin chartplotter or a Garmin Helm Control (GHC™ autopilot controller) along with dashes where the heading normally displays, it is due to one of two options. Most likely there is a third-party heading sensor aboard the vessel. If there is a third-party heading sensor, the autopilot needs to have the preferred sources set to utilize the Reactor™ autopilot CCU rather than the third-party heading sensor.
From a GHC™ 20 autopilot controller
Select Menu > Setup > Preferred Sources > Autopilot Heading Source - change to the Reactor CCU.
From a GHC™ 50 autopilot controller
From the autopilot screen, select 
> Autopilot Setup > Preferred Sources - change to the Reactor CCU.
From a current chartplotter1 compatible with programming the autopilot
From within the Autopilot screen:, select Options > Settings > My Vessel > Autopilot Setup > Preferred Sources - change to the Reactor CCU.
If the error is happening and there is no third-party heading sensor on the vessel, troubleshoot the network.
1Legacy chartplotters have different steps, see owner's manual for specific steps.