Date: 202003
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Dusk
Aircraft: Regional Jet 900 (CRJ900)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class C ZZZ
ATC / advisory: TRACON ZZZ; Tower ZZZ
Aircraft component: Autopilot
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Human factors: Workload; Troubleshooting; Distraction; Time Pressure
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Loss Of Aircraft Control
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Regained Aircraft Control; Flight Crew Landed in Emergency Condition; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Diverted; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Flight was uneventful until executing the localizer XXL approach into ZZZ.  It was Night VMC with a marine layer over the entire airport. Descending between 5000 ft. and 4600 ft. three Yellow Caution Messages suddenly appeared. After a few seconds; I instructed my First Officer to let ZZZ Tower know we needed to abort the approach due to caution messages.Tower instructed us to hold our altitudes; I proceeded to clean up the a/c; then the Tower vectored us around and finally transferred [us] over to Approach [Control]. First Officer advised ATC and Flight Attendants of our situation. At this time A/C was responding to all inputs accordingly; I transferred controls to First Office so I could reference the QRH.I decided to address the autopilot trim nose down first which stated to disengage the autopilot; re engage and monitor (AUTO 5). Prior to  following the procedure; I advised FO that there might be a heavy forward force pushing the yoke (as it was stated in QRH). After disconnecting the autopilot there was a very pronounced forward pitch which jerked the A/C very aggressively. FO countered the pitch down and I assisted him in trimming a/c until he was able to fine tune the trim. After we reengaged autopilot both Trim Caution messages disappeared however the Elevator Split still remained. Again A/C appeared to fly normally and follow inputs accordingly.At that moment; I conveyed to FO and company that we were diverting to ZZZ1 due to the caution message; better weather and not knowing how a/c would react again after disengaging the autopilot to land.  Additionally; the company Dispatch advised weather was clear at ZZZ1. Flight Attendants and passengers were briefed regarding my decision.We monitored our IECAS flight control page as we flew to ZZZ1 and all controls appeared normal. As we approached ZZZ1; I decided to advise ATC as a precautionary measure since I wasn't sure how the a/c would handle after disengaging the autopilot. Before landing we reviewed again the QRH and it stated to disengage autopilot; slow down below 200 kts. and 20 degrees of flaps. Furthermore; I requested a long final for runway XYR in order to prepare for any unexpected movements.  I took over controls at this point to execute the landing and fortunately A/C controls functioned as normal. The Brace Command was not requested.My only suggestion I can think about is that aircraft should always be returned to service ONLY after a flight check has been completed.  Especially after such a drastic movement has been experienced from a flight crew.


Second narrative: [Report narrative contained no additional information.]


Synopsis: CRJ-900 flight crew reported an autopilot malfunction with accompanying split elevator that resulted in a diversion.