Circuit Description

Supercharger boost pressure is regulated under certain conditions to prevent engine and drive train damage. When the engine is operating under high boost conditions, the engine control module (ECM) can limit boost pressure to 83 kPa (12 psi) or less.

The ECM disables boost under the following conditions:

When reverse gear is selected.
When an intercooler pump failure is detected.
When the intake air temperature (IAT) sensor 2 becomes excessively high, equal to or greater than 120.5°C (248°F) boost pressure is limited to 145 kPa (7 psi). The ECM commands the boost control solenoid to 62 percent duty cycle (DC).
When the engine coolant temperature (ECT) exceeds a predetermined threshold.
When drivetrain abuse is detected.
When vehicle speeds exceed 256 km/h (159 mph) in second, third, and fourth gears only, after 150 seconds boost is limited to a predetermined threshold.
When the intake cam phasers are inoperable, boost pressure is limited to 145 kPa (7 psi), ECM commands the boost control solenoid to 62 percent DC.

The ECM controls boost pressure by a pulse-width ground signal to the boost control solenoid. The boost control solenoid is a normally open valve. Under most conditions, the ECM commands the boost control solenoid to operate at a 99-100 percent DC. This keeps the boost control solenoid valve closed and allows only inlet vacuum from the supercharger plenum to the bypass valve actuator to control the position of the bypass valve. At idle, engine vacuum is applied to the upper side of the bypass valve actuator, counteracting spring tension to hold the bypass valve open. When the engine load is increased, the engine vacuum is decreased, causing the spring in the bypass valve actuator to overcome the applied vacuum, closing the bypass valve and allowing the boost pressure to increase. The bypass valve starts to close when the vacuum measure is 250 mm Hg (10 in Hg) and is fully closed at 90 mm Hg (3.5 in Hg). When reduced boost pressure is desired, the ECM commands the boost control solenoid to operate at a 0 percent DC, but may command a partial duty cycle, approximately 62 percent, depending on the operating conditions. This opens the boost control solenoid and allows boost pressure to enter the bypass valve actuator at the lower side to counteract the spring tension, opening the bypass valve, and re-circulating excess boost pressure back into the supercharger inlet.