As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 177 JFK-PHX, CREW DECLARED EMERGENCY AND AIRCRAFT RETURN BACK TO JFK DUE TO GPS PRIMARY LOST AND LOW ACCURACY INDICATED ON ND 1. MCDU HEADING INFORMATION DISPLAY ON ND WAS INACCURATE POS MONITOR AT GATE N4045.1W1159.7W N4038.4/W07346.7. PERFORMED NAV SYSTEM OPERATION CHECKS NO DEFECTS NOTED. REPLACED FMGC NR 2 AS PRECAUTIONARY REFERENCE AMM 34-10-00-34-14-00 AND 22-83-34. A/C OK FOR SERVICE.