NHTSA Preliminary Evaluation PE08016

IN MODEL YEAR (MY) 2007, PONTIAC SOLSTICE AND SATURN SKY VEHICLES EQUIPPED WITH THE 2.0L TURBOCHARGED ENGINE USED AN AUXILIARY VACUUM PUMP TO SUPPLEMENT THE ENGINE AS A SOURCE OF VACUUM TO THE BRAKE BOOSTER DURING LOW VACUUM CONDITIONS, SUCH AS IMMEDIATELY AFTER A COLD START.THE VACUUM PUMP OPERATION WAS CONTROLLED BY SWITCHES THAT SENSED BOOSTER VACUUM, TURNING THE PUMP ON WHEN BOOSTER VACUUM DROPPED BELOW A SPECIFIED LEVEL.IN THE MY 2008 SOLSTICE AND SKY VEHICLES (THE SUBJECT VEHICLES), GENERAL MOTORS (GM) ELIMINATED THE AUXILIARY VACUUM PUMP AND REPLACED IT WITH THE OPTIMIZED HYDRAULIC BRAKING (OHB) SYSTEM.THE DESIGN INTENT OF OHB IS TO SUPPLEMENT ENGINE VACUUM, IN CONDITIONS WHERE LOW VACUUM IS GENERATED BY THE ENGINE, WITH HYDRAULIC PRESSURE GENERATED BY THE STABILITY CONTROL SYSTEM PUMP CONTROLLED BY THE ELECTRONIC BRAKE CONTROL MODULE (EBCM). FOR UP TO ABOUT AMINUTE AFTER A COLD START, WHEN THE SYSTEM IS IN OHB ASSIST MODE, THE DRIVER MUST PRESS HARDER ON THE BRAKE PEDAL TO ACHIEVE DESIRED DECELERATION.ALSO, WHEN THE OHB MODE IS ACTIVATED, THE DRIVER CAN HEAR AND FEEL, THROUGH BRAKE PEDAL VIBRATION, THE STABILITY CONTROL SYSTEM PUMP OPERATION.STARTING IN LATE APRIL 2008, GM CHANGED FROM THE OHB SYSTEM BACK TO THE VACUUM PUMP SYSTEM DESIGN.ODI IS AWARE OF 264 NON-DUPLICATIVE COMPLAINTS TO ODI AND GM ALLEGING INADEQUATE BRAKE POWER ASSIST IN THE SUBJECT VEHICLES WHEN APPLYING THE BRAKES JUST AFTER A COLD START, INCLUDING ONE INCIDENT INVOLVING A CRASH INTO A TREE DURING A DRIVEWAY MANEUVER.TO ADDRESS THESE CONCERNS BY CONSUMERS, GM HAS ISSUED THREETECHNICAL SERVICE BULLETINS.ON JUNE 4, 2007, GM RELEASED AN INFORMATIONAL BULLETIN (NO PART REPLACEMENT OR SOFTWARE UPDATES), BULLETIN# 07-05-22-002, TO DEALERS EXPLAINING THE FUNCTIONALITY OF THE OHB SYSTEM.ON NOVEMBER 29, 2007, GM RELEASED A SERVICE BULLETIN, BULLETIN# 07-05-22-007, WITH INSTRUCTIONS TO RECALIBRATE THE EBCM WITH REVISED SOFTWARE TO MAKE OHB OPERATION FEEL MORE LIKE A NORMAL VACUUM ASSIST SYSTEM.TO I