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r107, r129, w198, w123, w124, w210
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116 Posts
Discussion Starter #1
I have recently noticed an annoying hum coming from ( what I believe to be the power steering unit) when i start my car. It lasts for about 10 seconds then goes away. Is my power steering pump going bad? I know it consumes a lot of fluid I have to add fluid about every 4 months. Do I have to replace the unit? Or is it something else? By the way the car is a 99 e300.
thanks
 

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E 420
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6 Posts
Usually if its you pump the noise will get louder when you turn the wheel. You should have it lifted on a rack and checked for leaks it shouldn't be using up fluid like that.
 

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03 E500
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120 Posts
RE: Annoying Hum when car is started..cooling fan test loop

The next time you start the car, open the hood first. Then, start the engine, and walk to the front of the car, and you will see that the cooling fans are both spinning on high for about 10 seconds, and then shut off. This is a self-diagnostic loop to test the fans every time the car is started.
Or is it a different sound you are describing?
Tom
 

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1997 E420 Sport
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262 Posts
This is normal.
It is the exhaust gas recirculating pump doing its job when the car is cold. It can start and stop a few times before the car reaches certain temperature. Once is warm it stops and the catalitics take the mission of cutting out emissions.
 

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r107, r129, w198, w123, w124, w210
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116 Posts
Discussion Starter #5
its a howling/whining noise and seems to only occur after I have driven somewhere stop the car and start it again i.e. when the engine is warm. It doesnt howl when the car has been parked for a while i.e when I start it in the morning etc. I really hope its the EGR thing but I am not sure.
 
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