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:

    Attaching the towing eyelet
    1 The towing eyelet is located under the floor of the cargo area, with the spare tire and may be partially concealed. This eyelet must be screwed into the positions provided on the right sides ...

    Impact protection
    The two front airbags are 'intelligent' and deploy in two stages according to the severity of the accident, alleviating the risk of facial injuries caused by the occupants' faces impacting with th ...

    Switching BLIS on and off
    BLIS is automatically activated when the ignition is switched on. The indicator lights will provide confirmation by flashing 3 times. • The system can be switched off by pressing the BLIS butt ...