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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 01-30-2010, 07:31 PM
Starless Starless is offline
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Post My troubleshooting and repair of codes P0491 & P0492.

If you are planning to remove your valve cover one day (for VCG or VANOS seals), you might want to read this just in case.

The following day after I was done with my VANOS seals kit installation, the SES light illuminated and the OBD 2 scanner informed me of 2 codes: P0491 and P0492. Great! The VANOS codes (P0014 and P0015) are gone and the secondary air control system codes are now registered. I'll explain later why it's not a coincidence. But at first I did not suspect it was related to my VANOS job. I went online and started reading on what the secondary air control system consists of. Air pump (not shown here), check valve (#1), solenoid vacuum control switch (#5), another little non-return valve (#6) and lots of vacuum line (#3,4,7) to connect these components as well as relays and fuses (not shown here).



Nice! How do I know which component is bad and causes the codes? Searched and found this very helpful document that describes the diagnostic procedures for every unit of the E46 secondary air control system. See pages 6 and 7 of this newsletter pdf:

https://www.bavauto.com/newsletter/2...newsletter.pdf

What follows is the abbreviated version of the diagnostic procedure that pertained to my specific case. Refer to the above-mentioned link for the complete protocol.

Step # 1: rule out the pump. Easy, mine works like a beast. Step # 2: rule out the check valve. Well, it does not seem to open...



Need to do the vacuum test. After a short trip to AutoZone I'm a happy owner of a MityVac hand vacuum pump. Now we'll see if the valve works or not. After an hour of trying to apply vacuum to the check valve, I realized that the MityVac vacuum pump the good people at AutoZone had sold me was defective: the vacuum release nipple was jammed. After fixing the vacuum pump I successfully applied vacuum to the valve, started the car and the valve opened, after releasing the vacuum it closed. So, the valve works just fine.



It's good news and bad news at the same time. The good news is that the 2 most expensive components are ruled out as perfectly working and the rest of the units are relatively cheap. The bad news is the fact that the rest of the components are located somewhere behind and under the manifold and I do not have a clear idea of how to reach them. So, to start with I decided to check the vacuum line going from the check valve to the solenoid vacuum control switch. The line runs around the valve cover and behind the manifold. You need to remove the cabin filter assembly and valve cover and fuel rail trim covers. And lo and behold! The vacuum line is disconnected at the little adapter that connects 2 hoses together, not even torn but just disconnected.



What happened is upon the reinstallation of the valve cover after the VANOS job I was moving the bundles of O2 sensor wires out of the way and inadvertently tugged at the hose disconnecting it. Did not even notice it at that time.



So that was an easy fix, the codes are gone. The moral of the story? Be careful with that vacuum hose back there when you remove and reinstall the valve cover. The hose also becomes brittle and brakes at the check valve but it's much easier to notice it there. So, although this all could have been avoided had I been more careful, it was a good experience and a chance to read up on how the secondary air control system works and it's diagnostic procedures.

Last edited by Starless; 02-04-2010 at 08:01 PM.
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  #2  
Old 01-30-2010, 09:00 PM
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16valex 16valex is offline
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Good job and thank you for sharing.
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  #3  
Old 01-31-2010, 07:47 AM
mujjuman mujjuman is offline
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That was a great read! and something to keep in mind wen doing this kind of work. thanks for sharing
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  #4  
Old 01-31-2010, 07:51 AM
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Well done!
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  #5  
Old 01-31-2010, 04:16 PM
Starless Starless is offline
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Originally Posted by 16valex View Post
Good job and thank you for sharing.
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Originally Posted by mujjuman View Post
That was a great read! and something to keep in mind wen doing this kind of work. thanks for sharing
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Originally Posted by G. P. Burdell View Post
Well done!
Thank you. These codes (P0491 & P0492) are pretty common and I hope this info will help people to DIY this repair. The diagnostic instructions in the bavauto newsletter are excellent. Hopefully there will be no need to take the car to the dealership just to get overcharged for...a piece of vacuum hose.
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  #6  
Old 01-31-2010, 04:24 PM
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When I got these codes I was happy to find it was actually the pump & the easiest thing, although maybe the most expensive, thing to replace. Another great writeup Starless.
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Old 01-31-2010, 04:37 PM
Starless Starless is offline
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Originally Posted by 968RACER View Post
When I got these codes I was happy to find it was actually the pump & the easiest thing, although maybe the most expensive, thing to replace. Another great writeup Starless.
I hear you. The pump is expensive but it's such a straightforward repair! Did you buy a brand new one?
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  #8  
Old 04-06-2010, 07:43 PM
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I could not edit my original post so I'm posting some additional information that I have collected here.

Paragraphs 6,7,8 and 9 of the bavauto secondary air system troubleshooting guide (see original post) discuss diagnosing system components located below and behind the manifold in a hard to reach place. Bimmerfest member Genuity shared the pictures of these components (electrical vacuum valve and non-return valve) that he took as a part of his car overhaul project. I appreciate his contribution and insert these pictures as a part of the origilal write-up.





Good luck!
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  #9  
Old 04-07-2010, 12:17 AM
BMW_325isedan BMW_325isedan is offline
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wow this got me looking at my car and i found out why the check engine light was on i thought it was because of the headers i had put on but ended up finding out when i had the codes read that it was P0491 and P0492 and that when i had put the headers on i for some reason never pluged that pump back in
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  #10  
Old 05-26-2010, 02:19 PM
gramirez gramirez is offline
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Alex, thank you so very much for your information WOW! its amazing on how much money i am saving...thank you, thank you..
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  #11  
Old 05-26-2010, 03:14 PM
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Alex, thank you so very much for your information WOW! its amazing on how much money i am saving...thank you, thank you..
No problem, just let us know how everything went and what was culprit of the codes
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  #12  
Old 05-26-2010, 03:44 PM
Nando779 Nando779 is offline
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Same exact thing happened to me when I replaced my valve cover. Saw the codes, wnet to autozone, got the codes read (vaccum leak), inspected and found the problem, bought a little piece of tube for about a buck and problem solved. Very nice write up as always Starless!
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Old 06-15-2010, 07:09 AM
gramirez gramirez is offline
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Alex, good morning, my car is fixed, thank you so very much for all the information/pictures you provided...Have a great day!
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  #14  
Old 06-22-2010, 11:24 AM
MrInternational MrInternational is offline
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After replacing the valve cover gasket, my car looks to have suffered from the same problems. (A tear in one of the vaccum lines) Where did you buy a new hose from? Did you replace the whole thing or just a small portion? Also, how did you fasten the new hose to the old one?

Thanks much!
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Old 06-22-2010, 02:05 PM
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Originally Posted by MrInternational View Post
After replacing the valve cover gasket, my car looks to have suffered from the same problems. (A tear in one of the vaccum lines) Where did you buy a new hose from? Did you replace the whole thing or just a small portion? Also, how did you fasten the new hose to the old one?

Thanks much!
Hi,

I used some vacuum line that came with the CVV kit from Tisher and that I never needed to use. And I replaced just a small piece and not the whole thing since it goes behind the manifold and there is no easy access. I think it can not be justified to buy the vacuum hose from the delearship though because it's highly overpriced and it's not any different than the one from a generic auto parts store. I'd take a sample and bring it to Auto zone or Advanced and it's going to be much cheaper. Where my hose disconnected I did not need to fasten anything. There was a small adapter that connected two ends of the hose.

Hope it helps.
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  #16  
Old 06-22-2010, 04:48 PM
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Awesome write up. Thank you for posting this. If I ever need this info. I'll know exactly what post to look for. Thank you Starless!.
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  #17  
Old 07-10-2010, 11:54 AM
MrInternational MrInternational is offline
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Originally Posted by Starless View Post
Hi,

I used some vacuum line that came with the CVV kit from Tisher and that I never needed to use. And I replaced just a small piece and not the whole thing since it goes behind the manifold and there is no easy access. I think it can not be justified to buy the vacuum hose from the delearship though because it's highly overpriced and it's not any different than the one from a generic auto parts store. I'd take a sample and bring it to Auto zone or Advanced and it's going to be much cheaper. Where my hose disconnected I did not need to fasten anything. There was a small adapter that connected two ends of the hose.

Hope it helps.
Where my disconnected, I did not have the rubber adapter so I went down to Lowe's and bought a 3/16" Barb x 3/16" Barb to act as a coupler between the two broken lines. When I connected the sample piece of hose, it seemed to work perfectly. Now I just have to wait for the car to cool down and try it out on the broken lines.
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  #18  
Old 07-10-2010, 01:31 PM
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The rubber hose popped off the hard plastic vacuum line (#3 in the diagram) and four codes came up: P1478, P1421, P1523, and P1423. I replaced the rubber vacuum hose, cleared the codes and they never returned.
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Old 07-10-2010, 01:34 PM
MrInternational MrInternational is offline
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The rubber hose popped off the hard plastic vacuum line (#3 in the diagram) and four codes came up: P1478, P1421, P1523, and P1423. I replaced the rubber vacuum hose, cleared the codes and they never returned.
Was it a pain to get back there? Did you have to remove a lot of stuff to do so?
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  #20  
Old 07-10-2010, 02:04 PM
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Was it a pain to get back there? Did you have to remove a lot of stuff to do so?
It wasn't the connection in the back, it was at the front; real easy.
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  #21  
Old 08-27-2010, 09:02 AM
LadyMysteriah LadyMysteriah is offline
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2000 323i air pump pressure hose CODE P1421

Alex,

Thank you for this post. My car thru the P 1421 code ans by reading this post with the pics I was able to find the hole, replace the hose with BMW for $27.50, and now I am good to go. I hope that was it.

Thanks,
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  #22  
Old 08-27-2010, 09:30 AM
Starless Starless is offline
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Alex,

Thank you for this post. My car thru the P 1421 code ans by reading this post with the pics I was able to find the hole, replace the hose with BMW for $27.50, and now I am good to go. I hope that was it.

Thanks,
No problem, glad it helped
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  #23  
Old 03-23-2011, 02:02 PM
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Sorry to revive an old thread but this is my exact problem. How long after separating the hoses behind the valve cover did you start to get codes? I did it a few months ago and it seems like only recently it started for me. I havent had a chance to check it cause of work, but planning on looking into it this weekend and was just curious as to timeline for this. Thanks for the DIY btw.
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Old 03-23-2011, 03:00 PM
Starless Starless is offline
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Originally Posted by moiz21 View Post
Sorry to revive an old thread but this is my exact problem. How long after separating the hoses behind the valve cover did you start to get codes? I did it a few months ago and it seems like only recently it started for me. I havent had a chance to check it cause of work, but planning on looking into it this weekend and was just curious as to timeline for this. Thanks for the DIY btw.
No need to say sorry, this thread is here to exchange opinions.

I got the codes like the next day. Before you assume it's the hose behind the VC, check the one by the check valve, check that the air pump kicks in in the morning, check the air pump large hose - those are easy things to do.

These codes might not even be related to the hose behing the VC, but it's a possibility too. It was in my case.
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Old 05-12-2011, 06:00 AM
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Great write-up. I just got these codes on my car yesterday, and like you, received them soon after changing my Vanos. For me, the small vacuum hose that attaches to the valve (#1 in the diagram) must have cracked after I moved these lines around. My hose turned into a hard plastic material that was extremely brittle. The cracking occurred where the hose met the valve connector.

I also checked the line behind the valve cover, but mine was still attached.

Went to a local auto parts store, but no one carried the 3.3 mm hose - everything they had was in standard units. I ended up picking up some 2.8 mm hose (7/64) which was fit (after some minor widening of the hole) over both the valve and the other vacuum hose (#3).

I scanned the OBDII with my Equus 3150 this morning and there were no codes. My CAT and EVA lights are still blinking and I'm receiving a yellow light for the emissions tests. I am assuming I will need to drive the car more before these reset themselves. Anyone have an idea of how long it takes before the system clears these lights (100 miles)?
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