As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NR 4 ENGINE N1 GAUGE IS INOP, CREW REPORTED THE NR 4 ENGINE N1 GAUGE WAS READING ZERO OR DASHES. AIR TURNBACK TO MSP. MAINTENANCE INSTALLED NEW N1 PICKUP, P/N 2-313-053-01, S/N OFF 001936018265, S/N ON 001936019832, CHECED ALL CANNON PLUGS SECURE RAN ENGINE OPS CHECK GOOD.