As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - INFLIGHT T2373/19 UPON TAKEOFF FROM MDW THE AIRCRAFT WOULD NOT PRESSURIZE AND THE STANDBY LIGHT ILLUMINATED. LANDED AT ORD WITHOUT INCIDENT. REPLACED NR 1 CONTROLLER. BITE CHECKED BOTH NR 1 AND NR 2 CONTROLLERS AND NO FAULTS NOTED. SYSTEM GROUND CHECKED NORMAL OPERATION.