What was found
AT FL 380 CAPTAINS MAP DISPLAYED VTK. LNAV AND VNAV DISCONNECTED. WE SWITCHED TO F/O'S SIDE OPS NORMAL LEFT FMC POSITION ERRATIC. GROUNDED - YES. LEFT FMC FAULT FOR PREVIOUS FLT FMC HAD RESTORED TO NML ON ARRIVAL. CYCLED FMC CMPTR-1 C/B, FMC OPS CKS PASS REF B737-800 AMM 34-61-00. DFCS FFR SHOWS MSG 22-11822 AND 22-11071 FOR PREVIOUS LEG, LRU TEST PASS REF B737-800 FIM 22-11 TASK 811. VERIFIED FMC POSITION PG STEADY.