As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DEN - FLIGHT 4331 - AFTER TAKEOFF, RECEIVED A PROX SYSTEM CAUTION MESSAGE. RETURNED TO FIELD AND ACCOMPLISHED A UNEVENTFUL LANDING. REMOVED AND REPLACED LANDING GEAR SELECTOR VALVE IAW CRJ700 AMM 32-32-10-000-801-A01/400-801-A01 CLEARED CAUTION MSG, OPS CK'D OK AND LK CK OK. AIRCRAFT RETURNED TO SERVICE.