Power brakes function only when theengine is running

Power brakes function only when theengine is running  - Brake system - Starting and driving - Volvo XC90 Owners Manual - Volvo XC90

The power brakes utilize vacuum pressure which is only created when the engine is running.

Never let the vehicle roll to a stop with the engine switched off.

If the power brakes are not working, considerably higher pressure will be required on the brake pedal to compensate for the lack of power assistance. This can happen for example when towing your vehicle or if the engine is switched off when the vehicle is rolling. The brake pedal feels harder than usual.

    See also:

    Getting started
    Use the controls on the steering wheel keypad and in the center console to access, navigate and make selections in the hands-free system’s menus. ...

    Marker lines
    The PAC system's lines 1 Marker line for a 1-foot (30-centimeter) zone behind the vehicle 2 Marker line for the clear back-up zone 3 "Wheel tracks" The solid line (1) indicates a zon ...

    Turn signals
    1. Remove the headlight housing from the vehicle (see page 306). 2. Remove the cover by pulling it straight out. 3. Pull the holder to access the bulb. 4. Press in the bulb and turn it to remove ...