As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON FLIGHT 3667 (DTW TO CTL) PERFORMED AIR RETURN TO DTW DUE TO NOSE DOOR OPEN AND GEAR DISAGREE MESSAGE. CREW DECLARED AN EMERGENCY. AIRCRAFT LANDED WITHOUT INCIDENT. REMOVED AND REPLACED NOSE LANDING GEAR CENTERED /EXTENDED PROXIMITY SENSOR BRACKET IAW DOWTY CMM 32-20-04. RE-INSTALLED PROXIMITY SENSOR IAW 32-61-05. PERFORMED EXTENSION/RETRACTION CHECK IAW AMM 32-30-00. ALL CHECKS GOOD.