Boost Pressure Reduction

Boost pressure is reduced in first gear and with RPM below 3000 RPM to reduce risk of wheel spin. Boost is also reduced if ECM registers that engine is near overheating. If the vehicle is equipped with an automatic transmission, the transmission receives information from the Transmission Control Module (TCM) about when reduced charge pressure is required, for example when shifting. On vehicles with an automatic transmission, there is also boost pressure reduction in the winter mode. If the vehicle is equipped with a manual transmission, the ECM determines which gear is selected based on the transmission and final drive gear ratios, engine RPM and vehicle speed.

Boost pressure can also be reduced to protect the engine from damage. If the knock sensors detect that the engine is knocking above a given threshold value, and ignition has been retarded and the air/fuel mixture has been enriched, the ECM will reduce boost pressure until the knock ceases.

Boost pressure will also be reduced if there is a risk of engine overheating. If the Engine Coolant Temperature (ECT) sensor indicates that the engine temperature has exceeded 244°F (118°C), the ECM lowers the boost pressure to reduce heat generation.