P0491 & P0492 (Secondary Air Injection System)
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  1. #1
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    P0491 & P0492 (Secondary Air Injection System)

    Hello.

    I'm a noob, so i might not know the right terminology but, i am having a bit of a problem with my 2002 V6 Passat. I have tried search, but it seems everyone is getting different answers.

    It all starts with the Check Engine Light coming on, Error Code P0491 and P0492. Since i work at Circuit City, i figured that there was just a faulty sensor and had one of the guys in the shop clear the error. I drove about five to six thousand miles, and bam it came back on again. So, again i had the guys clear the code for me.

    The next day, the light came back on again, it was the same code. I decided to take the vehicle to VW to see what was wrong.

    This is what the advisor put on the receipt:
    "Customer states combo values faulty bank 1-2/ SOP/Install Faulty Combi valves for secondary air INJ. SYS. Replaced both valves then ran basic settings and found the Vac. Solenoid not working properly. Replaced VAC. SOL. Then ran basic set. Again vehicle is now operation as designed."

    So since I'm just a young kid and know nothing about cars really, I whipped the credit card out and bought some valves, some solenoid, and some tubes.

    $600.00 later hoping the issue has been fixed, in the restored state that VW is the best, and bam, the next day the light came back on again...same error codes P0491 and P0492.

    Oddly, i have read that the secondary air system helps the car start (cold) and only runs for like ninety seconds, this error pops up usually when the AC is running in the car, and twenty minutes later....is that usual for error codes just to pop up randomly?

    I know the error codes stand for:

    P0491 Secondary Air Injection System Insufficient Flow (Bank 1)
    P0492 Secondary Air Injection System Insufficient Flow (Bank 2)

    But, what exactly does that mean....is it going to hurt the operation of my car if i don't repair it (the technician said it wouldn't hurt my car at all). Does it effect gas mileage? Because I don't think another $600.00 is worth it if it wont hurt my car.

    Thanks for the help,
    Mat.

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  3. #2
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    Rather than pay more money, take it back to the shop. They charged you $600, said the problem was fixed, but it wasn't. They should fix it and you should request that they do so at no additional charge. Read your receipt--likely their work has a warranty.

    I know that on the 1.8T that the combi valve can fail and leak corrosive exhaust gas/water into the secondary air pump, causing the pump to fail. If all they did was change the valve and not check the pump, then that may be the problem. I also had similar errors once due to a faulty relay for the air pump-- it is up next to the ECU on the 1.8T. Not sure about the 2.8 tho.
    Last edited by ClarkSJ; 05-03-2008 at 06:49 PM.

  4. #3
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    ClarkSJs correct, take the back and have them fix the problem as they said it was good. but:

    To answer some questions:
    1) it will not hurt the car if you do not fix it.
    2) it will not effect the gas mileage
    3) you will have a continuous Check Engine Light on

    Check your vacuum lines and replace them if they are the braided cloth type. These will not be covered under the warranty for previous repairs but should cost about $12 and an hour of your time. There is a good DIY writ-up here in the Info Base covering the V6 3.5 mm vacuum hose, preferably high temperature silicone if available. Also visually inspect the vacuum check valve in the system to make sure it is working. It looks like a small fuel filter in a vacuum line.

    One other suggestion, post your location, and engine, transmission etc in your profile. You may get better responses if you do.

  5. #4
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    Correct me if I'm wrong, but doesn't the secondary air pump affect emissions? Will he fail emissions with a bad one? (Actually, I think most states fail you if the CEL is on, anyway...)

  6. #5
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    Thanks for all the replies.

    GSO, I will take your profile advice. Until then though I have a 2002 Passat GLX Automatic V6. Thank you for answering those questions for me.

    Scotts, fortunately I live in Florida where there are no laws based on emissions.

    I am taking the car back to VW on Monday, I will be pissed they figured it was the wrong part. I will keep everyone updated.

    Thanks again,
    Mat.

  7. #6
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    As I understand the SAI system, the air pump provides excess air and the ECU supplies excess fuel during the initial 90-120 seconds from cold start to help heat the Cat to proper operating temperature quickly. Beyond that, the SAI system does very little for emissions. The SAI system occasionally operates, but again to get the Cat up to temp.

    As found searching here on PW, the solenoid, vacuum lines are common problems. Occasionally the Combination Valves (Combi/Kombi) are the issue, but not usually both valves (on a V6) at one time. That leads to vacuum lines or the solenoid valve. The relay or fuse for the power, located in the ECU enclosure, can also be issues and can lead to these codes for both banks.

    When the car is first started, do you hear the SAIP (pump) running. It sounds like a vacuum cleaner running for the first 90-120 seconds.

    Also check that the black plastic SAIP hoses not cracked and are connected on the discharge side.

  8. #7
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    Well I took the car back to the dealer, the problem is the piece they installed was defective.

    So they are replacing everything free of charge, so lets hope this works.

  9. #8
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    Quote Originally Posted by msweetnich View Post
    Well I took the car back to the dealer, the problem is the piece they installed was defective.

    So they are replacing everything free of charge, so lets hope this works.
    Hi msweetnich,

    Is everything working fine now? Just curious on you fix, I've had the same codes for over a year now. I replace the vacuum lines, the pump works fine, the only things I haven't changed was the combi valves and the solenoid that controls the combi valves.

  10. #9
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    Ive had the same codes as well. Longer than a year now

  11. #10
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    Hi e_andree,

    have you had to do a smog test with the CEL P0491 and P0492 codes? If so, did you just clear it before the test, and did you pass?

  12. #11
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    Quote Originally Posted by troz350 View Post
    Hi e_andree,

    have you had to do a smog test with the CEL P0491 and P0492 codes? If so, did you just clear it before the test, and did you pass?
    Yes, my car went through emissions last year and passed. Im not sure if MD testing is as stringent as CA though.

  13. #12
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    Ok, so I'm getting the P0491 and P0492 codes on my 2001.5 V6 Passat. Autozone couldn't make heads nor tales of it and the car is currently in a shop who's owner can't make heads nor tales of it.

    Would I be better off taking it to a dealership or doing this work myself?

    In all of the forums that I've been researching I've come to understand that these codes have something to do with the SAI System (specifically either a vacuum hose, solenoid, or combivalve)?

    One mechanic suggested that I change all of my spark plugs. I did after he cleared the CEL and the CEL stayed off for four days (100 miles), but came back on yesterday.

    I've also had O2 sensor CEL codes up last year, but they've seemed to disappear after the Cat was replaced. Are these two relatedin anyway?

    Thanks.

  14. #13
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    Same Thing Here

    oops repost.
    Last edited by vertigorillaz; 07-07-2008 at 10:04 PM. Reason: second post on the same subject, my mistake.

  15. #14
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    Check your vacuum lines and replace them if they are the braided cloth type. These will not be covered under the warranty for previous repairs but should cost about $12 and an hour of your time. There is a good DIY writ-up here in the Info Base covering the V6 3.5 mm vacuum hose, preferably high temperature silicone if available.

    Visually inspect the vacuum check valve in the system to make sure it is working. It looks like a small fuel filter in a vacuum line.

    Check the Vacuum Solenoid on the plate at the back of the intake manifold to verify it is working, meaning that vacuum is getting to the Combi Valves.

    Verify the SAI pump is working, in the initial 60-90 seconds from cold start-up, it sounds like a vacuum cleaner is running under your hood. If it is not working, check the fuse and relay first (mine is in the ECU box under the hood).

    Check that the Combi valves are opening under vacuum and air from the SAI pump can flow through them.
    Last edited by GSO_Passater; 07-08-2008 at 05:42 AM. Reason: spelling corrections

  16. #15
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    Video explanations of stuff would be cool if put on Youtube for everyone...

  17. #16
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    Had the same issue, i broke a vacuum line and used rubber tubing to bridge the connection for now until I can replace it with actual vacuum line and almost 24 hours to the minute the engine light pops back on P0491 and P0492 bank 1 and 2....Has anybody had this happen because of a broken vacuum line?...

  18. #17
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    I had the P0491 and P0492 code for 2 years, until I was force to fix it to pass smog. I replaced all the vacuum lines and the error still appeared. I always thought my secondary pump was working, since at a cold start the idle would drop down to around 800 rpm, which I thought that was what it did when the secondary pump went off. Then I decide to really check if the pump went ON, so I removed the corrugated hose that comes from the secondary pump below the front of the engine to above on the left front (as you stand in front) of the engine. On a cold start check to see if air comes out of the hose. If air doesn't come out of the hose I would check the relay 373 which is in your ECM box (in firewall by drivers side), which was the cause of my problem. This relay powers the secondary pump. I originally took out the pump to find out that it still worked after attaching 12 Volt to it. I would recommend checking the relay, since it's probably the easiest to fix. The relay is only $5 if you go to an auto parts store, but might not be easy to find, the guy at my local O'Reily's found a horn relay which is the exact same circuit relay. If you go to the dealer they may charge you alot more.

    good luck

  19. #18
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    I keep failing inspection for these codes, The terrorist state of NJ are tough on emissions, I just replaced relay 373 and now the pump is working again, I cleared the CEL and in exactly 24 hours it popped back on p0491 and p0492...Could any small vacuum leak cause these codes to come on and if i replace the vac lines will the code reset itself?..I cannot afford a new SAIP or kombi valves at this time so im hoping this is a quick fix

  20. #19
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    Vacuum lines, no, but the SAIP hoses aren't vacuum. Carefully inspect those two hoses - carefully because they're fragile, and inspect because they easily crack or split without it being obvious. If the pump is running and the hoses are intact, I'd look to the combi valve next. If everything is working the CEL should go off very shortly, as you found.

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