For 1990-2009 cars

# VACUUM PUMP SYSTEM SERVICE INFORMATION

VACUUM PUMP SYSTEM SERVICE INFORMATION-1982 CHEVROLET MODELS EQUIPPED WITH 4.4L (267 CU.IN.) V-8 ENGINE: THE FOLLOWING VACUUM PUMP SYSTEM SERVICE INFORMATION WAS OMITTED AND IS SUPPLEMENTED TO THE 1982 PASSENGER CAR SHOP MANUAL (ST-329-82), SECTION 5, BRAKES. REFER TO FIGURE 4. THE VACUUM PUMP IS DESIGNED TO AID THE ENGINE IN MAINTAINING A PROPER VACUUM LEVEL FOR THE POWER BRAKE SYSTEM. IT USES A PERMANENT MAGNET MOTOR AND VACUUM PUMP ASSEMBLY ENCLOSED IN AN INTEGRATED PLASTIC AND METAL HOUSING. EARLY PRODUCTION 1982 CHEVROLET VEHICLES WITH VACUUM POWER BRAKES AND VACUUM PUMPS ARE EQUIPPED WITH AN INTERNAL VACUUM OFF-ON SWITCH LOCATED IN THE PUMP ASSEMBLY. ITS FUNCTION IS TO ACTIVATE THE VACUUM PUMP WHEN THE POWER BRAKE SYSTEM VACUUM DROPS BELOW A DESIGNATED LEVEL . THIS SWITCH WILL BE ELIMINATED IN LATER PRODUCTION VEHICLES. WHEN THE INTERNAL VACUUM OFF-ON SWITCH SENSES A LOW VACUUM LEVEL IN THE POWER BRAKE SYSTEM, ITS SWITCH CONTACTS CLOSE, PROVIDING CURRENT FLOW FROM LOCATION "B" AT VACUUM PUMP TO THE SOLID STATE TIMER RELAY (LOCATED IN VACUUM PUMP HOUSING) WHICH ENERGIZES THE PUMP MOTOR. WHEN THE INTERNAL VACUUM OFF-ON SWITCH SENSES AN ADEQUATE VACUUM LEVEL IN THE POWER BRAKE SYSTEM ITS SWITCH CONTACTS OPEN DISCONTINUING CURRENT FLOW FROM LOCATION "B" AT THE VACUUM PUMP. BECAUSE OF THE SOLID STATE TIMER RELAY, THE PUMP MOTOR WILL STAY ENERGIZED FOR APPROXIMATELY 7-10 SECONDS AFTER THE VACUUM OFF-ON SWITCH CONTACTS OPEN. ALL 1982 CHEVROLET VEHICLES WITH VACUUM POWER BRAKES AND VACUUM PUMPS HAVE A VACUUM SWITCH LOCATED IN THE POWER BRAKE BOOSTER. THIS IS A DUAL FUNCTION SWITCH. THE SWITCH WILL SENSE VACUUM INTERNAL TO THE BOOSTER. WHEN A LOW VACUUM CONDITION IS SENSED, ONE SET OF CONTACTS IN THE SWITCH WILL CLOSE AND PROVIDE CURRENT FLOW TO LOCATION "C" AT THE VACUUM PUMP TO THE SOLID STATE TIMER RELAY WHICH ENERGIZES THE PUMP MOTOR. WHEN AN ADEQUATE VACUUM LEVEL IS SENSED IN THE VACUUM BOOSTER THE SWITCH CONTACTS WILL OPEN, THEREFORE, DISCONTINUING CURRENT FLOW TO LOCATION "C" AT THE VACUUM PUMP. BECAUSE OF THE SOLID STATE TIMER RELAY, THE PUMP MOTOR WILL STAY ENERGIZED FOR APPROXIMATELY 7-10 SECONDS AFTER THE SWITCH CONTACTS OPEN. THE OTHER FUNCTION OF THE SWITCH LOCATED IN THE VACUUM POWER BOOSTER IS TO ENERGIZE THE BRAKE WARNING LAMP. WHEN A LOW VACUUM CONDITION IS SENSED THE OTHER SET OF CONTACTS IN THE SWITCH CLOSE AND ACTIVATE A DELAY RELAY WHICH WILL TURN ON THE BRAKE WARNING LAMP. THE CONTACTS OF THE SWITCH WHICH ACTIVATE THE WARNING LAMP CLOS AT A LOWER LEVEL OF VACUUM THAN THE CONTACTS WHICH ACTIVATE THE PUMP.

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.