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General E46 Forum
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Old 12-12-2012, 08:02 AM   #1
Posh
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Noise under the bonnet (Hood)

Having switched the ignition on without starting the engine there is a sound under the bonnet (rather like a Computer cooling fan). Is this normal? I've had the car from new (2004) and never noticed it before.

Any suggestions?
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Old 12-12-2012, 11:12 AM   #2
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Originally Posted by Posh View Post
Having switched the ignition on without starting the engine there is a sound under the bonnet (rather like a Computer cooling fan). Is this normal? I've had the car from new (2004) and never noticed it before.

Any suggestions?
I just asked this same question a couple days ago and didn't get a firm answer. Seems like others have it as well. Does it turn off after a while or keep going? Does it continue for a bit after you remove the key? If so this is the same sound I have on my 323i, It seems to be comming from the throttle body area.
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Old 12-12-2012, 11:20 AM   #3
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are you asking whats the sound coming from the engine for the first 30 seconds of startup when the car is cold?

If yes, its your secondary air pump doing its work.
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Old 12-12-2012, 11:36 AM   #4
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are you asking whats the sound coming from the engine for the first 30 seconds of startup when the car is cold?

If yes, its your secondary air pump doing its work.
If it is the same noise I have it is not the SAP, it starts when the key is turned to the on position without the engine running. It comes from the opposite side of the engine as the SAP as well.
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Old 12-12-2012, 11:50 AM   #5
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Videos would help. Otherwise, we dunnnnnnnnnoooooooo
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Old 12-12-2012, 12:03 PM   #6
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If you have your heater set to on when you turn on the ignition (but not the engine), there's a small electric pump that might be running. Either under the heater valve or near the bottom corner of the rad (on e39s, not sure where it is on the e46 but assuming somewhere similar).

Also, the air conditioning system has blower fans as well as a small fan to sample cabin air. These might be running as well.

Last edited by pleiades; 12-12-2012 at 12:04 PM.
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Old 12-12-2012, 02:40 PM   #7
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^the secondary water pump is e39 only.

ICV? It's more of a buzz, though.
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Old 12-12-2012, 04:12 PM   #8
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Secondary water pump?
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Old 12-12-2012, 04:20 PM   #9
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You can see it in the middle bottom of the pic ^ ture. I think it's mostly to circulate warm coolant through the heater core so you can get a little extra heat after the engine is off. It also makes bleeding them much easier, as you can get 90% of the air out with the engine off.
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Old 12-12-2012, 04:36 PM   #10
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Fuel pump?
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Old 12-13-2012, 03:21 AM   #11
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Noise under the bonnet

Thanks for the suggestions. Applying a process of elimination: It's not the A/C and it doesn't go off after 30 seconds so not secondary air pump.

Looking at Icoleman's diagram it's coming from an area slightly further back in the engine compartment than the number "8".

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Old 12-13-2012, 10:53 AM   #12
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Sure seems to be the same sound I am getting. I am planning on taking parts off one be one this weekend till I get to the bottom of this. I'll let you know what I find.
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Old 12-13-2012, 10:55 AM   #13
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I think it's the ECU fan. If you put the key in acc, you'll hear a distinct "whirr" noise of a fan coming right from the box.
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Old 12-13-2012, 11:02 AM   #14
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ICV, like I said. Reach your hand down there and feel it. It should be vibrating.
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Old 12-13-2012, 12:02 PM   #15
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ICV, like I said. Reach your hand down there and feel it. It should be vibrating.
Where is the ICV at? I'm lost on these BMW engines
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Old 12-13-2012, 12:05 PM   #16
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Old 12-22-2012, 03:40 PM   #17
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Sure enough, the ICV was the culprit. Thanks a lot

Now, I would like to know if this constant buzzing sound is normal???
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