Circuit Description

Supercharger boost pressure is regulated to prevent engine and drive train damage. When the engine is operating under high boost conditions, the engine control module (ECM) limits boost pressure to 12 psi or less. The ECM disables boost under the following conditions:

• When reverse gear is selected
• When an electronic throttle control (ETC) fault is detected.
• 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). ECM commands the boost control solenoid to 62 percent duty cycle (DC).
• When the engine coolant temperature (ECT), is equal to or greater than 125°C (257°F), or the HOT engine light comes on.
• When drivetrain abuse is detected
• When vehicle speeds exceed 256 km/h (159 mph) in third and fourth gears, 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 duty cycle.

The ECM controls boost pressure by pulse width modulation (PWM) of 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 duty cycle. 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 diminishing applied vacuum, closing the bypass valve and allowing the boost pressure to increase. When reduced boost pressure is desired, the ECM commands the boost control solenoid to operate at a 0-98 percent duty cycle. This opens the solenoid valve and allows boost pressure to enter the bypass valve actuator at the lower side to counteract the spring tension, opening the bypass valve and recirculating excess boost pressure back into the supercharger inlet.

The ECM monitors the voltage level on the boost control solenoid control circuit. Refer to Boost Control System Description for further information.