As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RECEIVED A LANDING GEAR AIR/GND FAIL CAUTION MESSAGE DURING CLIMBOUT. COULD NOT BRING GEAR UP. MESSAGE EXTINGUISHED 2 MINUTES LATER. BROUGHT GEAR UP. LANDED BACK AT DEPARTURE, GEAR DOWN. REMOVED AND REPLACED NLG AIR /GROUND WOW PROXIMITY SENSOR NR 2 IAW AMM 32-63-02 OPS CHECKED GOOD IAW AMM 32-63-00.