What was found
CREW REPORTED LEFT ENGINE BLEED YELLOW MESSAGE EN ROUTE FROM CLT TO SDF. CREW RETURNED TO CLT AND LANDED WITHOUT INCIDENT. MAINTENANCE TROUBLESHOT AIR SYSTEM AND REMOVED, INSPECTED, CLEANED AND REINSTALLED THE FOLLOWING: PIPS (PACK INLET PRESSURE SENSOR) TUBE, PIFS (PACK INLET FLOW SENSOR) TUBE AND PDPS (PACK DISCHARGE PRESSURE SENSOR) TUBE. CHECKS WERE PERFORMED. ALL WORK WAS ACCOMPLISHED BY MAINTENANCE USING AIRCRAFT MAINTENANCE MANUALS. AIRCRAFT RELEASED FOR SERVICE.