As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
VTK ON CAPTS ND, MCDU WENT TO THE MENU SCREEN, ALT INFO DISAPPEARED ON CAPT PFD. RESET AFTER 30 SECONDS. APPEARED TO BE A LEFT FMC FAILURE EXCEPT LNAV/VNAV NEVER DISENGAGED. GROUNDED - YES. REF B737-800 FIM 34-61 TASK 801, PERFORMED FMC BITE TEST AND FOUND NO CURRENT FAULTS. REF FIM 34-61 TSK 836 FOUND TO BE INTERMITTENT FAULT. A/C OK FOR SERVICE.