check the pot and make sure it reads good, no hot spots in the readings, any glitch can trigger a fault.
also check real close the helical connector that connects the pot to the steering gear (if it is older style), they have been known to break , if newer style then the pot inserts directly into the gear, make sure the set screws are tight.

once you confirm the above conditions are satisfactory then run the steering calibration test in the information kevin sent you.

have fun ;o)