As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHIP 3133 - ATB - RETURNED TO SLC DUE TO AN APU EMERGENCY SHUTDOWN MESSAGE AFTER TAKEOFF. THE APU WAS NOT IN USE AT THE TIME OF THE MESSAGE. JAC OPERATIONS SHOWED NO AIR START CART AVAILABLE ON THEIR OPS PAGE. RETURNED TO SLC. CORRECTIVE ACTION: PERFORMED APU RESET/TEST AND FOUND NO LAST LEG OR PREVIOUS LEG FAULTS. PERFORMED MULTIPLE APU STARTS WITH NTF. (LP 5022382)