qsch,
First, let me state that I am NOT an Autopilot certified technician, but my wife finds me fairly handy!
I do not know if the flow sensor switch is supposed to be Normally Open (NO) or Normally Closed (NC) but to check it, you would need a multi-meter, or a battery powered continuity tester-
1. Disconnect power to the Autopilot unit panel
2. Unplug the sensor cable from inside the main panel, and check for continuity(very low resistance) from the flow sensor wires (pins 1 and 2, red and white wires) with the pump off and then on. If the sensor is working it will switch from open to closed(or closed to open) when there is enough flow to operate it.
3. If you do not see a change in continuity at the panel plug end of the wires, check at the sensor itself for the change.
If there is no change at the sensor itself, then it is bad, if the sensor changes, but not the plug end, then the cable could have a bad wire/connection, check it for cuts and kinks. If the sensor and the cable both are good, then make sure that plug to the panel main board is good and tight. All that is left that could be bad is the Main panel (which should have a 5 year warranty :-D .)
If the sensor itself is bad, you might be able to nurse the unit along by placing a jumper wire(or paper clip) from pin 1 to pin 2 on the main panel board, ***BUT*** the unit will not have any idea that there is NO FLOW when the pump is off and could turn on, causing unknown harm to itself and any objects nearby.
Since the flow and salt sensor both use the same cable, and you are getting both errors, the problem is likely in the cable, or its connections to the sensor or panel.
Best Wishes, and Good Luck!!!