My V50 2004/2005 has a pump in front the batery ( I believe vacuum pump) starts to work when the key is pluged and after aprox 3 min stop. The same happen after engine stop. No mensagem presents and the car works properly. My question is, what this pump does and what is the root cause of this problem? Is the pump or some sensor?
thanks.

 

The pump supplies vacuum to your brakes to allow for power braking when the car is cold. This is cause the engine has not had enough time to build up vacuum itself. After the engine warms up then the pump is no longer necessary. if the pump just runs for the hell of it yes there is a sensor that will screw up and cause it to think there is no vacuum and will cause the pump to just run like crazy