What is truble code PO551, Power Steering switch performance?

P0551-POWER STEERING SWITCH FAILURE When 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. I suggest replacing the power steering pressure switch first. It is a relatively inexpensive part and easy to replace. OTHER POSSIBLE CAUSES: (K10) POWER STEERING SWITCH SENSE CIRCUIT OPEN (K10) POWER STEERING PRESSURE SWITCH SENSE CIRCUIT SHORTED TO GROUND POWER STEERING PRESSURE SWITCH GROUND CIRCUIT OPEN PCM