As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHEN ON DOG LEG TO FINAL HEADING SELECT KNOB WOULD NOT CHANGE THE HEADING IN THE WINDOW. WHEN ON FINAL IT WORKED AGAIN. GROUNDED - YES. DUPLICATED PROBLEM, HEADING KNOB INTERMITTANT. REMOVED/REPLACED DFCS MODE CONT PNL PER B737-900 AMM 22-11-34, SYS OPS CKS NML PER SAME, GND VERIFICATION SUCCESSFUL.