What was found
AFTER TAKEOFF @ 1200 FT AGL FLAP POWER CAUTION ILLUMINATED AFTER ATTEMPTING TO RETRACT FLAPS. FLAPS REMAINED AT 15°. WE DID FLAP POWER CAUTION IN E&A FLAP POWER CAUTION EXTINGUISHED & RETRACTED TO 0° UPON LANDING ON TOUCHDOWN FLAP POWER CAUTION ILLUMINATED. DIVERTED. LANDING UNEVENTFUL. REMOVED FROM SERVICE. INTERROGATED CDS FLAP DRIVE SYSTEM. HYDRAULIC PRESSURE LOSS MESSAGE PRESENT. RESET C/B - FLAPS CONT (L ESS - L7). CAWP FLAP POWER CAUTION LIGHT EXTINGUISHED. C/W OPERATIONAL TEST OF WING FLAPS REF Q400 AMM TASK 27-50-00-710-801. OP CK FAILED. FLAP POWER CAWP LIGHT ILLUMINATED. PERFORMED OPS TEST OF WING FLAPS. CHECK FAILED AND FLAP POWER CAUTION ILLUMINATED AFTER 4TH CYCLE W/ BOTH SPU AND MULE. HYD PRESS LOSS CODE POSTED. PERFORMED GVI OF PRESS SWITCH, FPU, AND WIRING. NO DEFECTS NOTED. C/W Q400 HYD PRESS LOSS FIM TASK 29-10-00-810-803 PARA 1-4A.(2),5. PERFORMED OPS TEST 5 FULL CYCLES. OPS TEST GOOD, FAULT CODE DID NOT RETURN. NO DEFECTS NOTED. REPLACED FPU PRESS SWITCH REF Q400 AMM TASK 27-52-01-000/400-802, OPS CHECK GOOD.