B737-800
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
Flight Crew Overcame Equipment Problem
Aircraft
Turning to final for runway 9L; a 90 degree turn at 3000 feet with autopilot on; the autopilot reverted to CWS and the bank angle went to 45 degree before the autopilot was disconnected and roll was reduced. We stabilized the approach and continued to visual landing.  We are not sure the reason for the roll mode reverting to CWS but might have deselect heading select when turning the heading selector.
B737-800 Captain reported the autopilot reverted to CWS during a turn to final; and the bank angle went to 45 degrees.