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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 11-18-2012, 07:27 PM
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BM109R BM109R is offline
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P0491 code

Just finished washing the car today and as I was moving the car out of the wash bay I saw the service engine soon turned steady on. Checked the code and it was P0491. Looks like something to do with the secondary air system. Don't know much about this issue and searching confusing me even more. I just replaced the vcg and new spark plugs. I will check all the wires and hoses running alongside the valve cover to make sure all is connected well. Any pointers or tips on what else to check will be much appreciated. I cleared the code and drove around for about 15miles. Car drives fine.
Thank you.
BM109R

Last edited by BM109R; 11-18-2012 at 07:29 PM.
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  #2  
Old 11-18-2012, 08:12 PM
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So I just went out to check it out again(4hrs since I cleared code). All wires to sensors seem fine. Wire from air valve running along vc fine too. No SEL after starting the car. I hope no issues but still want to learn more about the code and the system involved.
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Old 11-18-2012, 08:44 PM
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16valex 16valex is offline
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What year and model is your E39? 528, 525, 530 or 540? It would be very helpful to state the specific model.

How the secondary air pump work?

When engine temperature is 85 degree F or below.
The ECU will send signal to the electric valve to allow vacuum to the air valve causes the air valve to open at the exhaust manifold and simultaneously send power to the air pump, the air pump then will send atmosphere air down into the exhaust system to help ease pollution.

Can you hear your air pump at first start in the morning when engine is cold?
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Old 11-18-2012, 08:44 PM
Steve530 Steve530 is offline
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There's a small plastic tube that runs along the right side of the valve cover with the oxygen sensor wires. This tube is connected to the SAP valve with a rubber hose and supplies vacuum to the SAP valve that opens a port to the exhaust when the SAP is running.

The rubber hose gets brittle and is easy to break. Since you just worked on the CG, I'd check that first. It's a3.5mm or 1/8" ID vacuum hose.

The other end of the tube connects to an electric valve with a rubber hose. This valve controls the vacuum supply.

The input to the electric valve is connected to a one-way valve with a rubber hose which is connected to a vacuum port on the intake manifold with another rubber hose.

When the ECU detects a cold start, it energizes the electric valve which supplies the vacuum to open the SAP valve through the tube and hoses. At some time, the ECU starts the SAP which blow air into the exhaust. The excess air causes the catalyst to heat up quicker. The ECU watches the oxygen sensors for the excess air. It it doesn't detect an increased oxygen level in the exhaust when the SAP is running it sets a DTC.
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  #5  
Old 11-18-2012, 08:49 PM
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Quote:
Originally Posted by 16valex View Post
What year and model is your E39? 528, 525, 530 or 540? It would be very helpful to state the specific model.

How the secondary air pump work?

When engine temperature is 85 degree F or below.
The ECU will send signal to the electric valve to allow vacuum to the air valve causes the air valve to open at the exhaust manifold and simultaneously send power to the air pump, the air pump then will send atmosphere air down into the exhaust system to help ease pollution.

Can you hear your air pump at first start in the morning when engine is cold?
My model is 03 530i. What type of sound should I be listening to hear at cold start?
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Old 11-18-2012, 09:00 PM
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Steve530, thanks for the explanation. I will check again and take a closer look at all the hoses with daylight. I think I can identify your explanations of the parts with the attached diagram. The only parts i just inspected are from the valve(1) to hose 3. I will remove the top plastic covers tomorrow and check the rest going to the electric valve. I don't remember if i clipped the rubber hose back to part 11&12.
Thanks!
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Last edited by BM109R; 11-18-2012 at 09:06 PM.
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  #7  
Old 11-18-2012, 09:00 PM
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Quote:
Originally Posted by BM109R View Post
My model is 03 530i. What type of sound should I be listening to hear at cold start?
A sound of an electric motor, it should be running for about 90 seconds. Or you can remove the bigger hose on the air valve quickly to check if any air is rushing out of the hose.
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Old 11-18-2012, 09:06 PM
Steve530 Steve530 is offline
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Originally Posted by 16valex View Post
A sound of an electric motor, it should be running for about 90 seconds. Or you can remove the bigger hose on the air valve quickly to check if any air is rushing out of the hose.
Yep, you'll be able to hear it from inside the car once you know what to listen for.
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  #9  
Old 11-18-2012, 09:08 PM
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Yep, you'll be able to hear it from inside the car once you know what to listen for.
Does it sound after I start the car or at ignition on?
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Old 11-18-2012, 09:13 PM
Steve530 Steve530 is offline
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Originally Posted by BM109R View Post
Steve530, thanks for the explanation. I will check again and take a closer look at all the hoses with daylight. I think I can identify your explanations of the parts with the attached diagram. The only parts i just inspected are from the valve(1) to hose 3. I will remove the top plastic covers tomorrow and check the rest going to the electric valve. I don't remember if i clipped the rubber hose back to part 11&12.
Thanks!
Those hoses are hard to reach, but if you lean way over and feel around you'll be able to confirm they are attached. Also note that the electric valve is actually mounted upside down from what is shown in the diagram.

The hose right at the valve is the real trouble spot. The others are probably OK.
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  #11  
Old 11-18-2012, 09:21 PM
Steve530 Steve530 is offline
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Does it sound after I start the car or at ignition on?
When the car is cold, it'll start a few seconds after the engine starts and run about 90 seconds, IIRC.

Open the hood, start the car, and walk around to the front. It will be noticeable.
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  #12  
Old 11-18-2012, 09:30 PM
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Quote:
Originally Posted by Steve530 View Post
When the car is cold, it'll start a few seconds after the engine starts and run about 90 seconds, IIRC.

Open the hood, start the car, and walk around to the front. It will be noticeable.
Thanks again. I will check it all out tomorrow.
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  #13  
Old 11-18-2012, 09:35 PM
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Let us know what you find out.
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  #14  
Old 11-20-2012, 07:52 PM
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So I finally got to check things out today. First, I couldn't identify air pump sound because my DISA is rattling and my idler pulley is whistling too. That's the next project for Friday. All belts , pulleys and a new DISA to be installed. The hoses looked fine along the valve cover. I used a telescoping mirror to peek at the electric valve end. All I see it the rubber hose looks old but all was attached as it should be. Today I drove the car for the first time since Sunday on multiple errands and runs fine with no service light on. I will probably look into replacing the rubber hoses and wire that view from the air valve to the electric valve soon. Looks like a tough DIY to get down there.
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  #15  
Old 11-20-2012, 08:18 PM
Steve530 Steve530 is offline
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Yep, you'll be working blind. I had to cut the hoses to get them off. Nothing light working blind in a tight space with a sharp knife to make you wonder if it's worthwhile.
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