What was found
CDU MESSAGE "CHECK FUEL AND GW" ILLUMINATED 3 TIMES WITHIN 2 MIN. UPON CHECKING PERF PAGE NO FUEL AMOUNT WAS SHOWING. THEN RETURNED TO NORMAL EACH TIME AFTER 30 SEC. GROUNDED - YES. DE-BRIEFED CREW. THEY DID NOT NOTICE ANY QTY IND ISSUES OR MISSING FUEL TOTAL ON DU WHEN MESSAGE OCCURRED. BITE CHECKED FQIS - LAST 2 LEGS FAULTED PROCESSOR. RMVD & RPLCD FQIS PROCESSOR UNIT REF B737-800 AMM 28-41-81. OPS NML PER SAME. FMC SENSOR PAGE SHOWS OK FOR FQIS. ETOPS GND VERIFICATION TEST SUCCESSFUL.