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:

    Turning ACC off completely
    From standby mode, press once. From active mode, press twice. The set speed and time interval are then cleared from the system's memory and cannot be resumed by pressing . ...

    Manual connection
    To connect a phone other than the one that was most recently connected or to switch between cell phones that are already paired with the hands-free system, go to Phone menu Change phone. ...

    RSE-AUX connectors and 12-voltsocket
    The three color-coded (yellow-white-red) RSEAUX connectors can be used to connect an auxiliary device to the RSE system. Always follow the connection instructions provided with the auxiliary devic ...