Boost Pressure Reduction

WARNING: This page is about a different car, the 2002 Volvo C70, 2001 Volvo C70, 2000 Volvo C70, 1999 Volvo C70, and 1998 Volvo C70. However, it is still accessible from the selected car via links, so may be relevant.

The charge pressure is reduced when driving in first gear and reverse with engine speed (RPM) below 3000 RPM to reduce the risk of wheel spin. If the engine has an automatic transmission the automatic transmission receives information from the TCM about when reduced charge pressure is required, for example when shifting.

If the car has a manual transmission the Engine Control Module (ECM) determines which gear is selected based on the transmission and final drive gear ratios, engine speed (RPM) and vehicle speed.

On cars with automatic transmission there is also boost pressure reduction in the winter mode.

Boost pressure can also be reduced to protect the engine from damage. If the knock sensors (KS) 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 Engine Control Module (ECM) will reduce the boost pressure until knock ceases.

A reduction in boost pressure also takes place If There Is a risk of the engine overheating. If the Engine Coolant Temperature (ECT) sensor indicates that the temperature has exceeded 118°C (244°F), the Engine Control Module (ECM) lowers the boost pressure to reduce heat generation.