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  1. #1
    mack
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    Codes PO 491 and PO 492 Secondary Air system

    I've had the Check engine light on for the last 3-4 days and recently got the codes scanned at Schucks that say

    PO491 Secondary Air Injection System Insuffiecient Flow (Bank 1)

    PO492 Secondary Air Injection System Insufficient Flow (Bank 2)

    I need help on trying to fix the problem myself before paying for a real mechanic. Any suggestions?

    The car runs fine! Its a 2001 325xi wagon with about 34,000 miles.

    Thanks

    Mark


  2. #2
    double vanos
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    I believe your seconday air injection pump has ..

    gone bad. There was a post here a while ago with a picture of the air pump and in the pic the rivets that held it together had popped. The secondary air pump is located on the passenger side of the engine compartment just ahead of the strut tower - it is a round black can looking device that pumps air into the exhaust manifold for emissions purposes. It has a relay that engages it and valve of some sort where it pumps air into the exhaust manifold. Got this from the Bentley manual. Hope it helps DV

  3. #3
    gscott2
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    Re: I believe your seconday air injection pump has ..


  4. #4
    gscott2
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    Another Possibility

    I recently also had the PO492 code appear. Having had my secondary air pump fail on a '97 E39 I was fearing the worst (and a $200+ part!).
    Turned out that the small black hose, 1/8 inch ID maybe, between the secondary air valve and the engine had hardened to the point of brittleness and had cracked. Replacing this hose seems to have fixed the problem.
    I saw an earlier post where someone had replaced their secondary air pump and it did not fix the problem. You can see if the pump is running by having someone start a cold engine while you stand near the secondary air pump and listen (cylinder near the windshield washer fluid reservoir). Noise and vibration from the pump should be noticeable for a minute or so, after which is will shut off. In the case of my E39 (where it did fail) there was no sound upon startup.
    Hope that helps anyone searching this topic in the future.

    '03 325iT 99k miles.

  5. #5
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    Re: Another Possibility

    Thats exactly whats wrong, little black hose that wires off the secondary pump may have cracked behind the engine, tight in there, if it is indeed cracked pulled the old one off and if a tiny bit stays on the nozzle, take a piece of sandpaper and rub it until it comes off. This little error happen to me but I did notice the hose was getting brittle and I ordered the hose and by the time it got it the car had starting throwing codes for the Secondary pump. Replaced and situation solved

  6. #6
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    Member No: 28239 bdaniel02 is an unknown quantity at this point bdaniel02's Avatar
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    PO Code 411

    I have this error @ service engine. The air pump works when cold start. Is this due to faulty air injection valve ?
    Thanks for any help or suggestions.

  7. #7
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    PO492 PO491 codes

    On My 330 2001, it also turned out that the small 3-4 inch black hose (1/8 inch) between the secondary air valve that runs next to the valve cover had hardened to the point of brittleness and had cracked needed to be replaced.

    For anyone else that gets these codes it could the pump, the air valve the hoses or the electronic valve or fuses???

    But researching these codes I found this great detailed expanation of how this system works:

    Once you get fault codes, it does not automatically mean that you have to replace parts. The FC's simply mean that you have problems in the circuits mentioned(in your case the secondary air systems in banks 1 & 2). You still have to diagnose the cause of the problem before you replace parts if needed.
    Sometimes you do not even need to replace anything(like when you just cut a vacuum hose with a loose end provided it still reaches its destination, or you just plug a connector that got loose).
    Your problem is with the secondary air pump system(the system in general since it involves both banks). At cold engine startup, the pump runs for about a minute to provide extra air into the exhaust system so that unburned gases gets burned off in the catalytic converter as part of the emissions system.
    The general overview of the system is this:
    1) the pump is turned on by the engine computer (DME) at cold startup
    2) the DME switches on the pump relay (usually found behind the glove box) which turns on the pump. The DME does its work properly when the 5 fuses in the main electronic box are not blown(the fuses are housed in a small box of 5 fuses). The small fuse box in turn is housed inside the big black box either on the left or right side of the engine compartment.
    3) if the pump does not turn on at cold startup then there may not be power at the connector to the pump or the pump itself is bad (or the pump may turn slower due to low voltage supply or due to a bad pump motor); you can feel and hear the pump running it is at the right somewhat front area of the engine compartment
    4) when running, the pump provides the air output thru a hose to a valve which is switched on by a vacuum switch solenoid (thru a small vacuum hose), usually the hose gets wornout and can no longer switch on the valve, sometimes the solenoid switch goes bad (this is at the left side rear end of the engine), sometimes the valve itself goes bad (you can test this by removing the valve, looking for free movement and functional testing by supplying vacuum to it)
    5) when the valve is working properly, then the air supplied by the pump goes into the exhaust manifold and then the catalytic converter
    6) the oxygen sensors before and after the catalytic converter monitors the situation during the brief span that the pump works (at cold startup) and then gives an OK or stores a fault as needed.
    So you see, it is not a simple matter. But with the above data you can diagnose the problem and find out for yourself what the car needs. It can be a fuse, relay, valve, solenoid switch, vacuum hose, or pump. But definitely not 02 sensors.

  8. #8
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    That Brittle black hose

    Does anyone have a picture of the hose that I hear gets brittle. I'm getting the same codes and do have a cracked hose exposing wires but not sure if they're the same ones others are speaking of. And my belief is replacing just the hose will cure problem? Appreciate the help.
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  9. #9
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    You're in luck (sort of). I just replaced that hose.

    Here is a picture of the secondary air injection pump - the large black cylinder. Below it (toward the front of the car) is a small silver and brass cylinder - the vacuum powered valve that's part of the secondary air injection system.



    Here is a closeup of the valve. The brass nipple sticking out from the right of the valve connects to the vacuum line.



    Lastly, here is the entire vacuum line removed from the vehicle:



    Note that the line is really 3 pieces. At each end are two traditional soft rubber vacuum hoses. The long middle is harder plastic, presumably more durable than rubber. I didn't realize that and removed the whole thing, replacing the entire thing with all rubber. It's likely you only need to replace the two short rubber pieces at each end, and not the long plastic tube.

    Both the rubber pieces broke off when I tried to remove them from their nipples. Additionally, there was a crack in the piece at the rear of the engine where it connects to the intake manifold (or really, some part of that giant vacuum complex that includes the oil separator). The crack was about 50% of the hose circumference and was causing serious idle problems and engine misfires.

    To access the hose at the rear of the engine, you will need to remove the fuel rail cover (one of the two plastic decorative engine covers), plus the cabin air filter and it's housing. I'd strongly also suggest removing the insulating panel between the engine compartment and the brake booster vacuum reserve. Otherwise, it's very difficult to access the nipple where the hose attaches.
    Last edited by oc330cic; 02-06-2013 at 08:04 PM.
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  10. #10
    bignick
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    po492

    i have the service manual for this car,and it doesent have this code in it..thanks for the help.anything not to bring the car to the dealer
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  11. #11
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    Big ups to this post.

    I have a 2001 325i and had trouble passing inspection. I just spent over 4k over hauling my suspension and was over due inspection by 1yr. After leaving the mechanic i drove directly to the inspection facility only to fail due to the readiness codes. Called my mechanic, who is very good, was informed to drive the car for ?? miles its possible sec air pump, or some o2 sensors which were both expensive jobs. I drove the car for approx 120 miles when the service engine light comes on. I go back to the shop to reset the codes and mileage. I was instructed to drive 75 miles and return to have the readiness codes checked, so i returned at 88 or so. The readiness codes had changed but not where they needed to be for the state inspection Iguess (texas). Was informed to drive home and back in the morning, if the light did not return, i was clear for inspection..... Cranked the car this morning, BAM...

    So I began to research the forums and came here. Just a random check this morning to check the hose referred and it cracked in half form a slight touch. Viola!!

    I had to post a reply here. Great job!!
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