NHTSA Preliminary Evaluation PE07018

DURING THIS INVESTIGATION, VOLKSWAGEN OF AMERICA (VW) IDENTIFIED A PROBLEM WITH WATER ACCUMULATION IN THE FRESH AIR PLENUM THAT COULD, IN CERTAIN CIRCUMSTANCES, RESULT IN REDUCED BRAKE POWER ASSIST IN MODEL YEAR (MY) 2002 PASSAT VEHICLES.VW INDICATED THAT PROBLEM IS CAUSED BY LEAVES AND OTHER DEBRIS CLOGGING THE PLENUM DRAINS, WHICH MAY RESULT IN WATER FILLING THE PLENUM TO THE LEVEL OF THE BRAKE BOOSTER AIR INTAKE.THE BOOSTER AIR INTAKE IS LOCATED IN THE FRESH AIR PLENUM IN THE MY 2002 PASSAT VEHICLES, BUT NOT IN THE MY 2001 OR 2003 VEHICLES WHICH DRAW BOOSTER AIR FROM THE CABIN.VW TESTING SHOWED THAT BRAKE ASSIST COULD BE REDUCED IF WATER ENTERS THE BOOSTER AND FREEZES.VW IS ADDRESSING THE PROBLEM WITH A SERVICE CAMPAIGN, WHICH BEGAN IN AUGUST 2007.THE FRESH AIR PLENUM IN THE SUBJECT VEHICLES IS AN ENCLOSED SPACE AT THE BASE OF THE WINDSHIELD FROM WHICH THE VEHICLE VENTILATION SYSTEM DRAWS THE FRESH AIR SUPPLY VIA A POLLEN FILTER.RAIN WATER THAT FLOWS OFF THE WINDSHIELD INTO THE PLENUM IS DRAINED THROUGH TWO VALVES LOCATED BELOW THE BATTERY AND BRAKE BOOSTER.STRAINERS AT THE BASE OF THE WINDSHIELD AND IN THE PANEL COVERING THE TOP OF THE PLENUM BLOCK LEAVES, PINE NEEDLES AND OTHER DEBRIS.OVER TIME, DEBRIS MAY ENTER THE PLENUM THROUGH OPENINGS IN THE PLENUM PANEL OR AROUND THE HOOD HINGES.IF CLOGGED DRAINS ALLOW APPROXIMATELY 3-4 GALLONS OF WATER TO ACCUMULATE IN THE PLENUM, THE WATER MAY ENTER THE BOOSTER THROUGH THE AIR INTAKE.WATER ACCUMULATION IN THE PLENUM MAY ALSO RESULT IN COMPLAINTS OF WET CARPETS IN THE VEHICLE INTERIOR IF THE WATER REACHES THE LEVEL OF THE FRESH AIR INTAKE/POLLEN FILTER. VW STATED THAT ITS TESTING SHOWED THAT BRAKE PERFORMANCE AND ACTUATING FORCE (I.E., PEDAL EFFORT) ARE NOT AFFECTED WHEN THE BOOSTER IS FILLED WITH THE MAXIMUM AMOUNT OF WATER POSSIBLE (UP TO THE HEIGHT OF THE BOOSTER ENGINE VACUUM CONNECTION, THROUGH WHICH WATER DRAWN INTO THE BOOSTER IS EVACUATED).VW'S TESTING SHOWED THAT BRAKE PERFORMANCE AND ACTUATING FORCE COULD BE AF