DTC P0574: Powertrain Control Module Detects High Vehicle Speed: Description
WARNING: This page is about a different car, the 2002 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
The cruise control module uses the cruise engaged circuit to request cruise control. If any condition exists that would make cruise control operation undesirable, the PCM will disable cruise control through the cruise inhibit circuit.