: Soft high frequency hum after shutting off car



carterb
10-13-12, 07:54 PM
Occasionally when I shut off my car after driving around, get out, close the door, I hear a very soft high frequency hum under the hood that stays on. When this happens, I usually get back in, restart the car, then turn it back off, and it usually resets with no hum. It is starting to do this more often - and I'm starting to listen for it more. Does anyone know what this might be? Would this potentially drain down my battery if I or my wife didn't catch it? This sound is relatively hard to hear - I can hear it in the garage though. Don't know if I would hear this out in a parking lot. The interior lights and everything else seem to shut off ok. No codes.

Any ideas ?

Carter

tedcmiller
10-13-12, 11:10 PM
The hum might be the fans that provide cooling continuing to run. They will do that if the engine temperature is above a certain point at shut down.

carterb
10-14-12, 11:13 AM
I am sure it is not the fans. It is the hum that sounds like when the headlights are on temporarily before they shut off.

STL09 V
10-15-12, 12:48 AM
It's your intercooler pump. Next time you hear it, pop the hood and look at the res. you will see fluid moving.

jzchen
10-15-12, 05:32 AM
I think I hear what you describe every once in a while. I think it has to do with opening and closing the doors and maybe even the trunk. (I don't use the car often.) I chalk it up to electronic noise, possibly from the proximity system for the keyless access system.

M5eater
10-16-12, 08:35 AM
It's your intercooler pump. Next time you hear it, pop the hood and look at the res. you will see fluid moving.
That would make the most sense, but I really don't understand why the pump would run after the car is shut-off. What difference does it make?

The afterun pump on the B5 S4 I had circulated coolant throughout the entire engine system, but that was to ensure the turbo's didn't cook the oil.

The only thing an afterun pump cycle on a supercharged car would do is cool-off the intercooler a bit. The rest of the aluminum is so hot that I'm not sure it would make a difference for cooling off the screws or anything of that nature either. The 10-15 degree drop of the I/C brick above the screws probably isn't going to overcome 190 degree aluminum block and heads surroudning the screws, or do anything really.

Cadillac Cust Svc
10-16-12, 10:53 AM
carterb,

If you continue to be concerned about this and decide to get this checked out by your dealership, please let us know as we're available to assist in that process as much as we can. We can be contacted either by private message or by email (katie_lucille@gm.com) - please include your name, contact information, and the last 8 digits of your VIN.

Sarah (Assisting Katie), GM Customer Service

STL09 V
10-16-12, 10:48 PM
That would make the most sense, but I really don't understand why the pump would run after the car is shut-off. What difference does it make?

The afterun pump on the B5 S4 I had circulated coolant throughout the entire engine system, but that was to ensure the turbo's didn't cook the oil.

The only thing an afterun pump cycle on a supercharged car would do is cool-off the intercooler a bit. The rest of the aluminum is so hot that I'm not sure it would make a difference for cooling off the screws or anything of that nature either. The 10-15 degree drop of the I/C brick above the screws probably isn't going to overcome 190 degree aluminum block and heads surroudning the screws, or do anything really.

I hear ya. I just know my does it and its the intercooler pump. If it hot where you are, next time you drive and turn off the V pop the hood and take a look. :)

SecretWeapon
10-17-12, 09:18 AM
Intercooler pump.