For 1990-2009 cars

# BRAKE BOOSTER LOW VACUUM SERVICE MANUAL UPDATE

THE INFORMATION IN THIS BULLETIN IS PROVIDED TO SUPPLEMENT THE 1982 BUICK CHASSIS SERVICE MANUAL. THIS INFORMATION IS BASICALLY FOR VEHICLES EQUIPPED WITH OVER DRIVE TRANSMISSION WHICH HAVE THE BRAKE BOOSTER LOW VACUUM INDICATOR CIRCUIT. 'PART B VACUUM CHECK PROCEDURE', CAN ALSO BE USED TO DIAGNOSE A LOW VACUUM CONDITION ON A VEHICLE THAT IS NOT EQUIPPED WITH THE LOW VACUUM INDICATOR CIRCUIT. DESCRIPTION OF LOW VACUUM CIRCUIT: BESIDES USING THE 'BRAKE' INDICATOR LIGHT ON THE INSTRUMENT PANEL ON SUBJECT VEHICLES TO WARN DRIVERS THAT PARKING BRAKE MAY BE APPLIED OR THERE IS A POSSIBLE PROBLEM WITH THE BRAKE HYDRAULIC SYSTEM, THIS LIGHT WILL ALSO INDICATE LOW BRAKE BOOSTER VACUUM. THE BRAKE BOOSTER LOW VACUUM CIRCUIT CONSISTS OF A VACUUM SWITCH LOCATED AT THE LEFT SIDE OF THE BOOSTER AND A MODULE LOCATED UNDER THE LEFT SIDE OF INSTRUMENT PANEL. REFERS TO FIGURES 1,2 AND 3. WHEN ENGINE IS RUNNING AND IF BOOSTER VACUUM IS BELOW APPROXIMATELY 12 INCHES, THE VACUUM SWITCH CONTACTS WILL CLOSE COMPLETING A GROUND CIRCUIT FROM THE SWITCH TO THE MODULE. REFER TO FIGURE 4. WHEN THIS OCCURS, THE MODULE WILL DELAY GROUNDING THE 'BRAKE' LIGHT FOR APPROXIMATELY 30-40 SECONDS. IF VACUUM REMAINS LOW FOR THIS PERIOD OF TIME, THE 'BRAKE' LIGHT WILL BE TURNED ON BY THE MODULE COMPLETING THE GROUND CIRCUIT. IN THE EVENT OF A 'BRAKE' LIGHT ON CONDITION THAT IS NOT CAUSED BY THE PARKING BRAKE SWITCH OR THE BRAKE HYDRAULIC SYSTEM, THE FOLLOWING INFORMATION IS PROVIDED TO DIAGNOSE THE LOW VACUUM INDICATOR CIRCUIT. DIAGNOSIS OF 'BRAKE' LIGHT 'ON' DUE TO LOW VACUUM CIRCUIT: FI BRAKE BOOSTER DOES NOT MAINTAIN VACUUM RESERVE FOR TWO (2) POWER ASSIST APPLICATIONS FIVE MINUTES AFTER ENGINE SHUT OFF, GO TO PART B - VACUUM CHECK PROCEDURE. A.CIRCUIT CHECK 1.WITH ENGINE IDLING IN PARK, UNPLUG BOOSTER VACUUM SWITCH CONNECTOR . A.IF 'BRAKE' LIGHT STAYS ON, REPLACE MODULE. B.IF LIGHT GOES OUT, GO TO STEP 2. 2.WITH JUMPER WIRE, SHORT ACROSS VACUUM SWITCH CONNECTOR TERMINALS. A.IF 'BRAKE' LIGHT GOES ON INSTANTLY, REPLACE MODULE. B.IF LIGHT COMES ON IN 30-40 SECONDS, GO TO STEP 3. 3.WITH ENGINE AT CURB IDLE, AND TRANSMISSION IN PARK, AND ENGINE VACUUM 13 INCHES OR MORE, CHECK CONTINUITY OF VACUUM SWITCH IN BOOSTER . A.IF SWITCH CONTACTS ARE CLOSED, REPLACE SWITCH. B.IF SWITCH CONTACTS ARE OPEN, SWITCH IS OKAY AND LIGHT 'ON' IS DUE TO WIRING. B.VACUUM CHECK 1.WITH ENGINE AT CURB IDLE, AND TRANSMISSION IN PARK, REMOVE CHECK VALVE FROM BOOSTER AND HOLD FINGER OVER END TO DETERMINE IF VACUUM IS AVAILABLE TO BOOSTER AND THAT CHECK VALVE OR HOSES ARE NOT LEAKING. A.IF THERE IS A LEAK, CORRECT AS REQUIRED. B.IF THERE IS NO LEAK AND VACUUM IS AT CHECK VALVE, REINSTALL VALVE IN BOOSTER, AND GO TO STEP 2. 2.ALLOW ENGINE TO RUN AT FAST IDLE A SHORT PERIOD (15 TO 20 SECONDS) AFTER CHECK VALVE INSTALLED, THEN TURN ENGINE OFF. 3.FIVE MINUTES AFTER ENGINE IS SHUT DOWN, AGAIN REMOVE VACUUM CHECK VALVE FROM BOOSTER. A.IF THERE IS A RUSH OF AIR, THIS INDICATES BOOSTER HAS VACUUM RESERVE AND IS NOT THE CAUSE OF LOW VACUUM. B.IF THERE IS NO AIR NOISE, BOOSTER HAS A LEAK AND SHOULD BE REPLACED, AS REQUIRED. NOTE: THE 'BRAKE' LIGHT WILL BE ON, SERVING AS A BULB CHECK, WHEN THE IGNITION SWITCH IS IN THE 'START' POSITION.

SECOND BULLETIN "LOW VACUUM WARNING SYSTEM - 1982 "J" SERIES" ALL 1982 CIMARRON MODELS WITH L46 ENGINES (VIN CODE G) INCORPORATE A LOW VACUUM SWITCH WHICH WILL TURN ON THE BRAKE WARNING TELL-TALE LIGHT IN THE INSTRUMENT PANEL IF VACUUM SUPPLY TO THE POWER BRAKE BOOSTER DROPS BELOW 6 TO 8 IN. HG. THE LOW VACUUM SWITCH SHOULD BE INCLUDED IN DIAGNOSIS OF A "BRAKE WARNING LIGHT ON" CONDITION. THE SWITCH HAS NO CONTROL OVER THE VACUUM PUMP WHICH SUPPLEMENTS ENGINE VACUUM AVAILABLE TO THE POWER BRAKE BOOSTER. LOCATION OF THE LOW VACUUM SWITCH IS SHOWN ON PAGE 5-3 OF THE 1982 CIMARRON SERVICE MANUAL AND FIGURE 1 OF THIS BULLETIN PROVIDES AN UPDATE OF PAGE 8A-52 (WIRING DIAGRAM).

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.