What was found
ON FINAL INTO DTW ON FLIGHT 3315, WITH SELECTED GEAR DOWN, HYDRAULIC CAUTION ILLUMINATED ONLY THE NOSE GEAR WAS DOWN. NOTED MAIN HYDRAULIC PRESSURE LOW AND ALL OTHER NORMAL. RAN QRH CHECK LIST, GOT THREE GREEN NORMAL LANDING FOLLOWED HYDRAULIC PUMP DOES NOT RUN IN AUTO OR OVRD. MAINTENANCE REMOVED AND REPLACED HYDRAULIC PUMP ASSEMBLY. ALL CHECKS GOOD AT THIS TIME.