This is documented in the DFC90 Pilot Guide 600-00252-000 (current revision):
- associated with the loss ADAHRS (dual PFD) 

- AP function is lost

First level troubleshooting is to re-rack the AP. Preferably by a shop. 

If re-racking does not resolve the issue, your tech will need to check the AP power/ground.

Shops with no access to the Avidyne Dealer Portal can email [email protected] for the Installation guide. 

Include the tail number, Aircraft make/model, document requested.