B737-800
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Flight Crew Overcame Equipment Problem; Flight Crew Took Evasive Action
Aircraft
Descending below 9;000; we received a TA (Traffic Alert). At approximately 7;000 feet; the indications turned into an RA (Resolution Advisory) conflict resolution. Aircraft indicated we were on a collision path with another aircraft and recommended that we climb. We looked for traffic while simultaneously disengaging the autopilot and auto throttle to comply with TA/RA. We descended to close to 7;000 followed by a climb to approximately 11;000. RA continued to indicate a climb. We queried ATC multiple times to see if they showed any traffic in our vicinity. They indicated that they showed an aircraft at 7;000 feet that was west and behind our position that should not have been a factor. Nonetheless; we climbed but the TA/RA still indicated a climb despite having climbed almost 4;000 feet. We deemed that this was an erroneous message. I took the controls to establish a descent and get us back to a path that would help us descend; but then we got a descent RA. We again complied with this RA just to be safe. After descending almost 3;000 [feet] and we still did not see any traffic; we determined that the aircraft was erroneously indicating a descent. We concluded that we were getting a malfunction. The aircraft had previously been written-up for a similar event just a few flights prior to our flights. The write-up had been cleared by Maintenance the morning of our flights. We flew the aircraft twice this day. The first flight was from ZZZ to ZZZ1 which we completed without any incident. However; the erroneous indications returned during the second flight from ZZZ1 to ZZZ2. After our conclusion; we returned the aircraft to normal flight; transferred the controls; and landed without further incident. Possible transponder malfunction. We wrote up the aircraft and discussed the event in great detail with Maintenance.
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B737-800 flight crew reported Traffic Collision Avoidance System Malfunction.