What was found
LEFT DUCT LEAK LIGHT ILLUMINATED EICAS MESSAGE LEFT BLEED DUCT LEAK DISPLAYED. LIGHT EXTINGUISHED AFTER ENGINE BLEED AIR SUPPLY AND ISOLATION VALVE CLOSED. TROUBLESHOT IAW FIM 26-18-10, SSM 26-18-01,& WDM 26-18-11. REPLACED M691 DUCT LEAK & WW CARD. RAN BOTH ENGINES & ISOLATE BLEED, FAULT REMAINS. CH & ISOLATED ELEMENT IN LT WING DUCT LEAK DETECTION LOOP'S FOR END TO END CONT. FOUND TS209 LOW ISOLATION. R & R TS209 DETECTOR ELEMENT IAW AMM 26-18-01-4. RUN BOTH ENGINES WITH N2 AT 80 PERCENT FOR 10 MIN & ISOLATED BLD AIR. NO FAULT NOTED.