Active Servo Unit, Pedal Pressure Sensor (DSTC only)

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2006 Volvo S80, 2005 Volvo S80, 2004 Volvo S80, 2003 Volvo S80, and 2002 Volvo S80. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Active Power Brake Booster, Pedal Pressure Sensor

Courtesy of VOLVO CARS OF NORTH AMERICA.

The servo unit is positioned on the bulkhead in the engine compartment. It consists of a vacuum cylinder (1), pedal position sensor (2), pressure build-up valve (3) and pedal pressure sensor (4). The pressure build-up valve and the pedal pressure sensor (activation unit) have a common connector which cannot be replaced.

The pedal pressure sensor is positioned in the servo unit and provides the brake control module (BCM) with information about brake activity. If the driver presses the brake pedal during stability control, the control module will take account of this.

The active servo unit is controlled by the brake control module (BCM) and builds up an initial brake pressure. This is so to allow braking during active yaw control. An active brake pressure is obtained within 0.1 seconds. This occurs without the driver needing to brake. The pressure build-up valve opens and allows atmospheric pressure to enter the rear chamber in the servo unit. The brake pressure sensors (5) continuously monitor the brake pressure. The pulse width controlled pressure build-up valve in the servo unit maintains the brake pressure at approximately 10 bar during stability control.