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Discussion Starter · #1 ·
2012 Cruze Eco

I have had this car for 5+ years. I am one of those guys who listens to the starter motor humming and starts the car after the humming stops.
Yesterday, I noticed that the humming does not stop. If I leave the key in position 2, the humming goes on until I turn the ignition to start. On turning the ignition, the car starts fine and seems to run fine. The humming does stop (or, so I think).

The only thing that changed was that I re-activated OnStar yesterday morning. Could that have updated something that changed the behavior? Or, is something about to break?

The battery was on its last leg, so I went ahead and replaced it yesterday to eliminate any problem with the battery.

Thanks !
 

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Did you recently refill your vehicle? Was it low on fuel? There are a lot of things it could be, from a clogged fuel filter to a faulty pump; what we really need to know is how the car behaved after it started.
 

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Probably the vacuum assist pump for the brakes.

Does it sound like this?

 

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Discussion Starter · #6 ·
Oops ! I feel stupid ! Yes, the fuel pump priming. Sorry ! The car does seem to be running fine. It is not low on gas. It was filled 3-4 days ago. I will watch how it is running.
 

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Discussion Starter · #7 ·
jblackburn, on your video, were you referring to the sound at the last 2 seconds of the video? I think that is what I hear. I will check again tonight.
 

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jblackburn, on your video, were you referring to the sound at the last 2 seconds of the video? I think that is what I hear. I will check again tonight.
You (I) can hear it throughout the entire video when I hit the brake pedal.

If the little pump is constantly running, there's a vacuum leak to the brake booster somewhere. It should build up a vacuum, then shut off.
 

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Discussion Starter · #9 ·
No, it is not the brake assist vacuum. I don't have to hit the brake pedal to get the noise. I don't hear it after the engine starts (or it blends into the engine noise). It is almost like the fuel pump starts priming and doesn't stop. The car runs fine, so I am going to ignore it for now.
 

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Have you had the HVAC reset yet? What you describe kinda sounds like it could be the #PI below. For me I could hear it with the car on and off if it's a quiet night or inside an enclosed area(garage). The brake booster pump I never really hear unless i'm pressing on the brakes between windows 1 and 2 of a drive thru with the window still down.

#PI1267 High Pitched Whine or Buzz Noise From Engine Compartment After Engine is Turned Off.
 

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Discussion Starter · #11 ·
No, it is not PI1267. This is only before starting the engine. There is no noise after stopping the engine. And, air conditioner is off.
 

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Discussion Starter · #12 ·
I have tracked the noise down to the vacuum assist pump.
Thanks, jblackburn. You were right.

The noise is from the vacuum assist pump. I hear the noise when the key is in START position (engine not started; brake not pressed). The noise stops after starting the engine. Then, I can hear it momentarily when I pump the brake. It stops immediately afterwards. Doesn't sound like it is continuously running (once the engine is started).

Could this be a bad vacuum assist pump? Could it be a leak? Wonder why it is constantly running before the engine starts.
 

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I have tracked the noise down to the vacuum assist pump.
Thanks, jblackburn. You were right.

The noise is from the vacuum assist pump. I hear the noise when the key is in START position (engine not started; brake not pressed). The noise stops after starting the engine. Then, I can hear it momentarily when I pump the brake. It stops immediately afterwards. Doesn't sound like it is continuously running (once the engine is started).

Could this be a bad vacuum assist pump? Could it be a leak? Wonder why it is constantly running before the engine starts.
If it stops once engine is started, and only runs when brake is pressed that is normal.

Running while off - I'd suspect a bad check valve in the line to the brake booster or the little vacuum "reservoir".
 
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