The contact owns a 2015 Cadillac CTS. The contact stated that occasionally while driving at various slow speeds, the message ‘Driver Assist Unavailable’ and the steering wheel was abnormally firm, requiring excess effort to drive the vehicle until the power steering functionality returned. There was no warning light illuminated. The vehicle was taken to a local dealer, where the vehicle was diagnosed; however, the contact was advised that there was no failure found with the vehicle, and the failure was not duplicated. The vehicle was not repaired. The contact referenced NHTSA Campaign Number: 25V175000 (STEERING); as a possible cause for the failure. The manufacturer was not notified of the failure. The approximate failure mileage was 92,000.