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 82.7 kPa (12 psi) or less. The ECM limits or disables boost under the following conditions:
- Reverse gear is selected
- Electronic throttle control fault is detected.
- An intercooler pump failure is detected
- Engine Coolant Temperature (ECT), is equal to or greater than 125°C (257°F).
- Drivetrain abuse is detected
- When intake air temperature (IAT) sensor 2 is equal to or greater than 120.5°C (248°F), the ECM commands the boost control solenoid to 62 % duty cycle and boost pressure is limited to 145 kPa (7 psi).
- When vehicle speed exceeds 256 km/h (159 mph) in third or fourth gear, boost is limited to a predetermined threshold after 150 s.
The ECM controls boost pressure by pulse width modulation of the supercharger bypass solenoid valve, which is normally open. Under most conditions, the ECM commands the bypass valve 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 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 between 0 to approximately 62 % 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.