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:
- Reverse gear is selected.
- Intercooler pump failure is detected.
- Electronic throttle control fault is detected.
- Intake air temperature (IAT) sensor 2 is equal to or greater than 120.5°C (248°F). Boost pressure is limited to 145 kPa (7 psi).
- Engine coolant temperature (ECT) is greater than 125°C (257°F).
- Drivetrain abuse is detected.
- Vehicle speeds exceed 256 km/h (159 mph) in second, third or fourth gear for greater than 150 s.
The ECM controls boost pressure by a pulse-width modulated (PWM) ground signal to the supercharger bypass solenoid valve. The bypass valve is a normally open valve. Under most conditions, the ECM commands the bypass solenoid to operate at a 99-100 % duty cycle. This keeps the bypass 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 is 33.9 kPa (10 in Hg) and is fully closed at 11.9 kPa (3.5 in Hg). When reduced boost pressure is desired, the ECM commands the bypass solenoid to operate at a 0 % duty cycle, but may command a partial duty cycle, approximately 62 %, depending on the operating conditions. This opens the bypass 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.