Automatic High Altitude Compensation
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.
Because the Engine Control Module (ECM) determines boost pressure using the signal from the intake air pressure sensor, there is automatic boost pressure control compensation when driving at altitude and in different temperatures. The engine power is not therefore noticeably affected by air density or temperature.
When altitude exceed 2000 meter above sea level the engine control module (ECM) cannot compensate boost pressure any further because the air is too thin.