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  1. #1
    Active Member One Ring
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    P0491 & P0492 Troubleshooting

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    Just bought a 2004 S4 a couple of weeks ago, 46,000-ish miles. The first cold morning, before the car was completely warmed up I got a check engine light. Read the codes and got P0491 & P0492 which says Secondary Air System Bank 1 & 2.

    Cleared the codes, and drove for several days without any issues. Then last night I took a drive, about 15miles or so, and after the temp gauge was to the normal range, I got a check engine light again. Again the same two codes.

    I have done some searching, but have not really found all the info about this system. I know it injects fresh air into the exhaust so that the cats get to optimal working condition sooner. But I was surprised to get the fault after the car seemed to be warmed up, does anyone know when and for how long this system is active? Any quick checks, or known problem areas?

  2. #2
    Registered Member Three Rings tylerS's Avatar
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    Aug 02 2009
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    Re: P0491 & P0492 Troubleshooting

    per yahoo answers:

    "PO491 or 16875 is a Secondary Air System fault Bank 1. Bank 1 refers to the passenger side off the engine. The combination valve for secondary air injection did not preform as it should & set a fault. The valve is located under the plastic engine cover at the rear of the right cylinder haed. There is a plastic tube from the air pump to the valve that breaks, the valve sometimes fails, there is a vaccum hose that opens the valve that also sometimes fails & rarely the Air Injection Vacuum Control Solenoid Valve fails. The plastic tube unpluggged/cracked or failed valve are the 2 most comon failures I see. Beond that there isn't much you can test using a generic scantool. If you have a factory VW/Audi or VAG-COM scantool I can give you more help. Good luck UPDATE>>>> If it's a vac leak it's in the small hose from the solenoid valve to the combination valve. The super charger may affect the vaccum, but I would exspect to see more codes if it was really messing with things.. The air injection system only runs for about 1.5 minutes on cold starts. If the plastic tube is broken you will hear what sound like a small exhaust leak. What mods have you done to this thing. You may want to invest in a VAG-COM if you are tuning it yourself. It's pretty cheap. http://www.ross-tech.com/ It makes dealing with VW/Audis much easier. You have a generic code reeader of some sort, but I'm sure there are other codes stored that won't show up with out VAG scan capabilities.
    Source(s):
    ASE Master Tech. VW/Audi Tech. 20+years exp."

  3. #3
    Active Member One Ring
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    Thanks

    Some of that is useful info, what car was the answer directed towards, supercharged S4? But why would my check engine light come on 15 min. into the drive? And I know that it was longer than a 1.5 min time span before it went off the first time.

  4. #4
    Registered Member Three Rings tylerS's Avatar
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    Re: P0491 & P0492 Troubleshooting


  5. #5
    Active Member One Ring
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    Re: P0491 & P0492 Troubleshooting

    I know how to look things up on google. I was looking for more specific answers.... but thanks for showing me posts I've already read.

  6. #6
    Registered Member Three Rings tylerS's Avatar
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    Re: P0491 & P0492 Troubleshooting

    you're welcome buddy

  7. #7
    Veteran Member Three Rings mad70sx's Avatar
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    Re: P0491 & P0492 Troubleshooting

    Quote Originally Posted by chockrl View Post
    I know how to look things up on google. I was looking for more specific answers.... but thanks for showing me posts I've already read.

    Good luck getting help in the future with that attitude,chief.

  8. #8
    Senior Member Two Rings blkonblkS4's Avatar
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    Providence, RI

    Re: P0491 & P0492 Troubleshooting

    Quote Originally Posted by chockrl View Post
    I know how to look things up on google. I was looking for more specific answers.... but thanks for showing me posts I've already read.
    Well thanks for the update on what you have tried thus far genius. What a terd.

  9. #9
    Veteran Member Four Rings jfunkey's Avatar
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    Re: P0491 & P0492 Troubleshooting

    Quote Originally Posted by blkonblkS4 View Post
    Well thanks for the update on what you have tried thus far genius. What a terd.

    hahhaaaahaha 2nd

    Bro chockrl be thankfull you got that much info.

    regardless good info tylers.

    But to try and help more. Check vac leaks and then try tapping on the can with a small hammer. There is a valve in there and some times they get stuck..
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  10. #10
    Active Member One Ring
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    Re: P0491 & P0492 Troubleshooting

    Guess I was looking for more first hand knowledge, on a B6/7 S4. VW and Audi both use this system but the layout and potential problem area's are different.

    Vacuum leaks and sticky valves are the first things I'll check. Anyone else see the problem come up after the cars already warm? Seems like the system should not be active.

  11. #11
    Active Member Two Rings
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    Re: P0491 & P0492 Troubleshooting

    Are you using a VAG or a generic code reader?

  12. #12
    Account Terminated Four Rings
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    Re: P0491 & P0492 Troubleshooting

    "Hey guys need help"

    (help given)

    "That help sucks. Need better help"

    (more help given)

    "That help sucks too"
    __________________________________

    Wow.

  13. #13
    Active Member One Ring
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    Re: P0491 & P0492 Troubleshooting

    Generic code reader

  14. #14
    Active Member One Ring
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    Re: P0491 & P0492 Troubleshooting

    Found the root cause of my fault codes. After checking a lot of things and figuring out where everything is routed and how it is supposed to work.

    Checked:
    Secondary Air Pump runs on cold startup - yes
    Solenoid on front of engine sends vacuum at startup - yes
    Each combination valve holds vacuum - yes
    Entire vacuum line setup from solenoid holds vacuum - yes
    Secondary air pump supply is attached to air box - yes

    Note: Secondary air pump is located just behind the bumper on the passenger side, if you remove the skid plate it is right there.

    Secondary air pump supply is attached to pump - yes
    Secondary air pump pressure side is attached to pump - yes
    Secondary air pump pressure side hose connection to back of engine - no

    There is a connection along the passenger side head, under the passenger side radiator hose and near the front corner of the air box. This is where I found my problem, the hose clamp was not there and the hose had became disconnected. The combination valves were not getting any secondary air pump flow.

  15. #15
    Active Member Two Rings bguevarra's Avatar
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    Sep 22 2009
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    west la

    Re: P0491 & P0492 Troubleshooting

    just got these 2 codes today. gonna get it checked out tomorrow. will update the results.

  16. #16
    Active Member Two Rings bguevarra's Avatar
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    Re: P0491 & P0492 Troubleshooting

    so i talked to the audi dealership in long beach and they found that my secondary air pump had failed which was throwing the CEL. he mentioned that it isn't a common problem, but it does fail from time to time, or leak, or become disconnected. just a quick swap in and out which should take about 2 hours once they get the part in.

    in any case, it's a $750 job at no cost to me since i just got it on halloween. i just have to wait until monday. i've never missed any of my cars as much as i already miss this one. haha

    sweet.

  17. #17
    Active Member Two Rings Tre5's Avatar
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    Quote Originally Posted by chockrl View Post
    Found the root cause of my fault codes. After checking a lot of things and figuring out where everything is routed and how it is supposed to work.

    Checked:
    Secondary Air Pump runs on cold startup - yes
    Solenoid on front of engine sends vacuum at startup - yes
    Each combination valve holds vacuum - yes
    Entire vacuum line setup from solenoid holds vacuum - yes
    Secondary air pump supply is attached to air box - yes

    Note: Secondary air pump is located just behind the bumper on the passenger side, if you remove the skid plate it is right there.

    Secondary air pump supply is attached to pump - yes
    Secondary air pump pressure side is attached to pump - yes
    Secondary air pump pressure side hose connection to back of engine - no

    There is a connection along the passenger side head, under the passenger side radiator hose and near the front corner of the air box. This is where I found my problem, the hose clamp was not there and the hose had became disconnected. The combination valves were not getting any secondary air pump flow.
    Hey, Thanks for the help. I had these same codes and I would have had to search even longer to find the pump if it wasn't for this thread. I was able to trace the hose from the pump up to the area behind the engine, under the intake. It was there that I found my problem... the body shop had somehow twisted the hose on re-installation (pulled a lot of things out of the engine compartment to get the new color under the hood).

  18. #18
    Senior Member Three Rings p3u's Avatar
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    Rocky Mtns
    Items for Sale

    Quote Originally Posted by tylerS View Post
    per yahoo answers:

    "PO491 or 16875 is a Secondary Air System fault Bank 1. Bank 1 refers to the passenger side off the engine. The combination valve for secondary air injection did not preform as it should & set a fault. The valve is located under the plastic engine cover at the rear of the right cylinder haed. There is a plastic tube from the air pump to the valve that breaks, the valve sometimes fails, there is a vaccum hose that opens the valve that also sometimes fails & rarely the Air Injection Vacuum Control Solenoid Valve fails. The plastic tube unpluggged/cracked or failed valve are the 2 most comon failures I see. Beond that there isn't much you can test using a generic scantool. If you have a factory VW/Audi or VAG-COM scantool I can give you more help. Good luck UPDATE>>>> If it's a vac leak it's in the small hose from the solenoid valve to the combination valve. The super charger may affect the vaccum, but I would exspect to see more codes if it was really messing with things.. The air injection system only runs for about 1.5 minutes on cold starts. If the plastic tube is broken you will hear what sound like a small exhaust leak. What mods have you done to this thing. You may want to invest in a VAG-COM if you are tuning it yourself. It's pretty cheap. http://www.ross-tech.com/ It makes dealing with VW/Audis much easier. You have a generic code reeader of some sort, but I'm sure there are other codes stored that won't show up with out VAG scan capabilities.
    Source(s):
    ASE Master Tech. VW/Audi Tech. 20+years exp."
    I am having this problem. Car sounds like it has an exhaust leak maybe 1 out of 10 times I drive. If it were a cracked tube Id assume it would do it all the time. With that said any thoughts on it doing this occasionally?
    2004 S4 Avant, Goodwood Green, JHM intake manifold, JHM spacers, Stratmosphere intake, 034 Intake hose, JHM tune, Piggies, Magnaflow exhaust, JHM brake kit, Team Dynamic 1.2 Wheels, B5 perches, 034 snub, PC680 battery, 991 oil and coolant caps, Euro black optic grilles, Votex roof spoiler, RNS-E HD.
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  19. #19
    Registered Member One Ring
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    Is this covered under audi factory warranty?

  20. #20
    Registered Member One Ring
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    Is this covered by audi factory warranty

  21. #21
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    Was this covered under factory warranty?

  22. #22
    Veteran Member Three Rings
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