HSA is an electronic parking brake, which is directly connected to the main brakes and the ESC system. It automatically prevents the vehicle from backsliding on inclines by activating the normal brakes.
This application requires very high performance sensor for the measurement of the longitudinal inclination of the car. The basic performance is better than ±3°, which requires better than 50mg stability of the accelerometer over the temperature range and lifetime. The OEM may apply so called 'auto offsetting' at the end of the car assembly line in order to reset all assembly errors and the software in the ESC's ECU may offset the signal after certain intervals. With a sophisticated lifetime autozero algorithm only the offset temperature dependency remains limiting the system performance, as long term effects can be zeroed out.