Yes, that is an issue with the Power steering switch circuit.
The switch is the most likely cause but there is always a possibility of the problem being in other components of the circuit.
Here's the official flow chart tests for that code. This is designed to eliminate all possibilities for the code.
SYMPTOM P0551 - POWER STEERING SWITCH FAILUREWHEN MONITORED With the ignition key ON and engine running.SET CONDITION With the vehicle above 40 mph for over 30 seconds , the power steering pressure switch remains open.POSSIBLE CAUSES power steering pressure switch ground circuit open
Yes, the truck is safe. It's just that the computer is not seeing a signal from the power steering switch. It does this like pause the A/C and increase the idle when it sees high pressure.
L1 Master Technician
ASE Mastertech with Adv level Engine performance cert.