Crownie is right about checking for steering movement during start-up (selftest) also make sure you have a good woodruff key on that new steer motor that was just installed. Whats happening is the steer module wants to see movement of the steering within a window of time via the feedback encoder. If you suspect the the feedback encoder is not counting + and - you can swap it with the steertiller one on the platform as they are the same. Hope this helps? Let us know what you find.

when you turn key, quickly run to front of unit and see if steering moves or have a helper cycle key
clean the relays behind the plastic cover under the traction panel
could be the steer controller, these are notorious for unusual faults
could be wear in steering gearbox (attached to motor)