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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #1  
Old 12-16-2007, 05:21 PM
DM3MD DM3MD is offline
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What is an air pump? What does it do?

Hi guys,

On my service record (I'm now the second owner), it stated some 5,000 miles ago "Air pump failed---permanent malfunction; replaced"...

What does an air pump do? How did the original owner know it failed? Is it common for them to fail so quickly? The search function focuses A LOT on water pumps, but not air pumps...

Thanks from the novice...
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  #2  
Old 12-16-2007, 06:41 PM
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The air pump is part of your exhaust emissions (EGR) system....it brings in fresh air to aid in more complete combustion of burned gasses. A failing pump can trigger a frequent CEL, as well as fouled spark plugs (which causes rough running).

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Bob
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  #3  
Old 12-17-2007, 04:48 AM
sierrakilo99 sierrakilo99 is offline
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The air pump does most of its duty right after startup, trying to minimize excess emissions from cold start and idle. You'll hear it (its fairly loud) when you first crank it up, after a few seconds, it should kick off. I would think the previous owner saw a SES light and the DTC code showed it was bad when read by the dealer.
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Old 12-20-2007, 10:43 PM
njoni007 njoni007 is offline
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Your pump pressurizes the crankcase and aids the intake with extra O2 needed while the engine is running rich in fuel (extra HP/torque is required when engine is started the first time or in cold start). In winter the air pump stays longer running while in summer it turns on or sometimes may not even turn on at all.

It is very unlikely to fail but nothing is impossible. I would say don't even worry about it and sleep free as well as drive worry free. When it breaks come here for help before you go to stealership.

If there was Automatic transition problem that is where I would worry or engine problems such as burning oil and hard starts when hot (sign of compression problem).
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Old 12-21-2007, 03:21 AM
Narcisse91 Narcisse91 is offline
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Quote:
Originally Posted by Fast Bob View Post
The air pump is part of your exhaust emissions (EGR) system....it brings in fresh air to aid in more complete combustion of burned gasses. A failing pump can trigger a frequent CEL, as well as fouled spark plugs (which causes rough running).

Regards,
Bob
I've never looked at the BMW setup, but on previous cars with air pumps, they was pumping air into the exhaust PAST the primary O2, right before the first cat. If the air pump failed, the CEL may pop up because the emissions system wouldn't be working, but I would think it would have no real affect on how the car drove. The BMW system would have to be pumping air before the first O2 sensor, which seems like a stupid way to do it. In my experience, the air pump is something that can be removed with no impact on how the car drives.
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Old 12-21-2007, 10:25 PM
alpinewhite325i alpinewhite325i is offline
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Quote:
Originally Posted by njoni007 View Post
It is very unlikely to fail but nothing is impossible.
Not exactly.

On older e46's they are prone to fail.
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