Have you checked the transistor modules behind the power card? The code is an open in the field circuit. Could be bad cable connections on the motor, a power card, a bad TM. First step is make sure your motor circuit is good. Remove the S1 and S2 cables from the power card and test from one to the other and make sure you have very low resistance. Make sure you don't have shorts to frame on them either. Check the power card and TM's as per the book.