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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 98 (ENGINE CONTROL SYSTEM TESTING & ENGINE COMPONENT TESTING)AIR INDUCTION SYSTEMSBOOST CONTROL SYSTEM (BONNEVILLE, GRAND PRIX, PARK AVENUE & REGAL)DESCRIPTION
1999 GMC Forward Control 5.7 R, Automatic

Boost Control System (BONNEVILLE, Grand PRIX, Park Avenue & Regal): Description

1999 GMC Forward Control 5.7 R, AutomaticSECTION Description
WARNING: This page does not describe the selected car, but rather 31 other vehicles, including the 2002 Saturn SL2, 2002 Saturn SL1, 2002 Saturn SL, 2002 Saturn SC2, and 2002 Saturn SC1. However, it is still accessible from the selected car via links, so may be relevant.

The boost control solenoid is a normally open valve. Under most conditions, the Powertrain Control Module (PCM) commands the boost control solenoid to operate at 100 percent duty cycle, which closes the solenoid valve to allow the system to boost. This is achieved by allowing manifold vacuum to reach the top port of the bypass valve actuator through the inlet vacuum signal hose. With the boost control solenoid closed, vacuum from the boost source hose can not reach the lower port of the bypass valve actuator to disable boost. However, if reverse gear is selected, the PCM detects deceleration, engine temperature is extremely high, or drive train abuse is detected, then reduced boost pressure is desired. Under these conditions the PCM commands the boost control solenoid to operate at 0 percent duty cycle, which opens the solenoid valve and allows vacuum to pass from the boost source hose, through the boost control solenoid and boost signal hose, to the bypass valve actuator lower port. This disables boost by opening the bypass valve. With the bypass valve open, boost pressure is reduced by recirculating intake air back through the supercharger inlet.

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