REDUCED BRAKE POWER-ASSIST

SAAB AUTOMOBILE AB, A SUBSIDIARY OF GENERAL MOTORS CORP. (GM), MANUFACTURED 12,317 SUBJECT VEHICLES THROUGH FEBRUARY 15, 2008, EQUIPPED WITH THE "HIGH FEATURE" V6 TURBOCHARGED ENGINE IDENTIFIED BY REGULAR PRODUCTION OPTION LP9. A TANDEM VACUUM BRAKE BOOSTER ASSEMBLY PROVIDES BRAKE POWER-ASSIST. THE ENGINE IS THE PRIMARY VACUUM SOURCE TO THE BOOSTER AND ITS EFFECT IS AMPLIFIED BY A VENTURI. UNDER CERTAIN CONDITIONS, SUCH AS A COLD ENGINE START OR AT HIGH ALTITUDES, AN ELECTRIC VACUUM PUMP (EVP) SUPPLEMENTS ENGINE VACUUM. A PRESSURE SWITCH MEASURES BRAKE BOOSTER VACUUM AND COMMANDS THE EVP WHEN TO TURN ON/OFF. CHECK VALVES ARE LOCATED AT THE INTAKE MANIFOLD, VENTURI, AND PRESSURE SWITCH. GM IDENTIFIED TWO ISSUES THAT AFFECT EVP PERFORMANCE: CORROSION OF ELECTRICAL COMPONENTS INSIDE THE PUMP CAUSED BY MOISTURE INGRESS THROUGH THE AIR OUTLET WHEN THE EVP SHUTS OFF AND THE VACUUM IN A SECTION OF PIPING BETWEEN THE EVP AND THE PRESSURE SWITCH IS RELEASED TO THE ATMOSPHERE; AND SILICONE CONTAMINATION OF THE ELECTRICAL CONTACTS INSIDE THE PRESSURE SWITCH RESULTING IN A NOISY OR IMPEDED ELECTRICAL SIGNAL. GM ADDRESSED EVP PERFORMANCE WITH TWO DESIGN CHANGES. IN NOVEMBER 2007, GM MODIFIED THE RUBBER PROTECTIVE CAP THAT COVERS THE EVP AIR OUTLET TO IMPROVE SEALING AND IN FEBRUARY 2008, GM ADDED A CHECK VALVE TO THE SECTION OF PIPING BETWEEN THE EVP AND THE PRESSURE SWITCH AS CLOSE AS POSSIBLE TO THE EVP IN AN EFFORT TO REDUCE THE BACK FLOW OF MOISTURE THROUGH THE PUMP. IN TOTAL, THE OFFICE OF DEFECTS INVESTIGATION (ODI) IS AWARE OF 240 SUBJECT VEHICLES AFFECTED BY THE ALLEGED DEFECT. COMPLAINANTS REPORT THAT SYMPTOMS OCCUR IMMEDIATELY AFTER A COLD ENGINE START AND ONLY FOR A SHORT DURATION (30 TO 60 SECONDS), DURING WHICH PERIOD THE AMOUNT OF BRAKE POWER-ASSIST PROVIDED TO THE OPERATOR MAY BE REDUCED DUE TO AN INOPERATIVE EVP. THE SYMPTOMS MAY BE MORE PRONOUNCED THE LONGER THE VEHICLE HAS BEEN PARKED AS THERE IS A NATURAL TENDENCY FOR THE BRAKE BOOSTER TO SLOWLY RELEASE THE VA