As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING ACCOMPLISHMENT OF T/C 78273000 NR 1 ENGINE HAS FAULT MSG 78-21541 EACH REVERSER SLEEVE HAS ONE POSITION SIGNAL OUT OF RANGE THIS IS A SHORT TIME 50 FLIGHT HOURS FAULT. GROUNDED - YES. REF FIM'S 78-36T808, 75-34T815, & 75-22T802. ACCOMPLISHED RESISTANCE CKS. NO DEFECTS NOTED. PER FIM, REPLACED NR 1 ENGINE EEC REF B737-800 AMM 73-21-60. GROUND VERIFICATION SUCCESSFUL REF AMM 73-21-00.