So what pump/motor is running under the hood

As soon as my d wakes up (open door), there is something running under the hood. It also continues to run for many minutes after the car is shut off. I think it's the aux water circulating pump but have no idea why it would be running. Does this happen to your d? It's not very loud but something is running.

Could well be the vacuum pump running in anticipation of starting.
Lots of pumps on these cars.

Didn't think about the vacuum pump, but believe it's mechanically driven (that cylinder looking thing on the front of the engine?). But does everyone else's do this?

no idea what pump it is. I thought its some kind electronic equipment. I also know its not specific to d. Coz it also happens in 335i and 328i.

Originally Posted by KeithS

Didn't think about the vacuum pump, but believe it's mechanically driven (that cylinder looking thing on the front of the engine?). But does everyone else's do this?

You're right, the vacuum pump is on the exhaust camshaft.

Just went down for the paper - opening the door starts what sounds like an electronics (ECU) cooling fan on the right side firewall. Something else going when shutdown. I've heard them both before. And last night when I came home and unloaded the trunk, sounded like the SCR transfer pump was running after shutoff.

Only sound I ever notice before turning on the car is the sound that reminds me of a computer booting up. Seems like it happens as soon as a door or trunk is opened and eventually if the engine is not started it sounds like a computer shutting down. I can't remember if the 328i loaner cars did it or not but always wondered if it maybe was the cause for some people's battery drain issues.

Yes, I have heard a number of different sounds, both when entering the car and then when getting out.

I've heard the electric cooling fan for the radiator when I shutdown, that is normal.

I've heard the fuel transfer pump or something like that in the rear of the car both when starting up and shutting down. Also normal.

I think I've heard something related to the DPF when I shutdown, that is very sporadic so assume perhaps it was in middle of it's cycle when I shutdown. Expect that is also normal.

Can't say I have heard anything abnormal other than the loud squeal of the fan belt, which has now been resolved with the new belt, thank you very much.

Every time I get into the car where it is in a quiet location, I hear the car hard drive spinning up.