As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
A/P #A DISENGAGES AFTER 5 SECONDS TRIED 3 TIMES. A/P B WORKS OK. GROUNDED - YES. A/P "A" HAS CHAN-A AIL SYNC INV <4 SEC FAULT MSG 22-11189. NO FAULTS ON A/P "B". REPLACED THE "A" AILERON AUTOPILOT ACTUATOR PER B737-900 AMM 22-11-25/401. OP-CHECKS GOOD. DURING THE TESTING, FOUND THE AILERON POSITION SENSOR OUT OF RIG. ADJUSTED PER AMM 22-11-29-820-801.