Code 52 pump motor open circuit had it many times most likly brushes or cable on brush gear motor will have to come out as cant check or replace brushes in situ is worth checking current sensor but have never had one go down good luck

Check the right hand speed sensor and the circuit back to the logic card. If o, the fault is probably in the logic card. To check you could swap the card into another truck if you have one available.
Correction, misread your post error 52 I described is for an FB16KT not an FB15 model, your fault is the pump motor