As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LAX - POWERPLANT MESSAGE ON TO. RETURN TO FILED. LANDING UNEVENTFUL. INTERROGATED CDS FOUND FAULT CODE 338B BOTH ENGINES. CLEARED PEC CODES IAW AMM TASK 61-20-36-070-801. PERFORMED GROUND RUNS ON BOTH ENGINES MULTIPLE TIMES, UNABLE TO DUPLICATE POWERPLANT MESSAGE. NO FAULTS NOTED IN CDS AFTER RUNS. SCHEDULED EMU FOR DOWNLOAD. RETURNED TO SERVICE. NO PARTS REPLACED.