Depends on the date of manufacture of the particular ship. The older NGs inhibit FEEL DIFF PRESS if flaps are not up, it is always available on the newer ones. could mean that the actual feel computer has failed, that its inputs (the elevator pitots) have failed or that the hydraulic pressure differential exceeded 25% for more than 30 seconds.
Oh, and there is more to say about the PTU: Its supposed to aid the (very weak) electric B pump in extending and retracting the LED and more importantly ensures rapid autoslat operation to prevent an imminent stall, even if normal sys B quantity has been lost (since it retains some liquid) until the first deployment.