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Discussion Starter · #1 · (Edited)
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/2008_n408_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.
 

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Discussion Starter · #5 ·
Good job and thank you for sharing.
That was a great read! and something to keep in mind wen doing this kind of work. thanks for sharing
Well done! :thumbup:
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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Discussion Starter · #7 ·
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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Discussion Starter · #8 ·
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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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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Discussion Starter · #11 ·
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 :thumbup:
 

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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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Discussion Starter · #15 ·
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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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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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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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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