As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IAH - FLIGHT 2139, THE CREW REPORTED THAT THE LEFT LANDING GEAR UP INDICATIONS ARE INDICATING RED IN THE UPLOCK POSITION. THE AIRCRAFT RETURNED TO IAH WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE REMOVED AND REPLACED THE UPLOCK PROXIMITY SWITCHES, OPERATIONALLY TESTED WITH NO DEFECTS, AND THE AIRCRAFT WAS APPROVED FOR RETURN TO SERVICE.