What was found
APPROACHING ETOPS ENTRY AT 35,000 FEET "MASTER CAUTION-FUEL" ANNUNCIATOR ILLUMINATED ALONG WITH LEFT CENTER TANK "LOW PRESSURE" LIGHT. RAN 'FUEL PUMP LOW PRESSURE' CHECKLIST. OPENED CROSSFEED VALVE AND MOVED LEFT FUEL PUMP SWITCH TO OFF. GROUNDED - YES. AIR TURNBACK - TROUBLESHOT LH CENTER TANK BOOST PUMP. REMOVED AND REPLACED LH CENTER TANK BOOST PUMP PER B737-800 AMM 28-22-41-000-801, AND AMM 28-22-41-400-801. GROUND VERIFICATION CHECKS GOOD PER AMM 28-22-41-710-801.