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:

    Power windows
    Driver's door control panel 1 - Switch for disengaging rear door power window buttons 2 - Rear door window controls 3 - Front door window controls. WARNING Always remove the ignitio ...

    Operating DAC
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    Spin control (SC)
    The spin control function is designed to help prevent the drive wheels from spinning while the vehicle is accelerating. ...