This is usually down to the steer controller which is mod 6 or the steer motor.
Remove the motor cables off the steer control unit which sits behind the seat, and check the U,V,W on the unit between the supply pos or negative on the unit and those connections with a digital multimeter on diode test. You may find 1 of the phases is short or open circuit. They usually read identical if ok. Test the motor cables to chassis for shorts and check between the phases on the motor for open circuit. Those are basic checks that can be carried out.