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Thread: BMW E46 "Check filler cap" light is on, intermittently

  1. #1
    Administrator ucfbrett's Avatar
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    Default BMW E46 "Check filler cap" light is on, intermittently

    Ugh, this car. Another round of parts thrown at the car, visits to the BMW dealership and the local German shop have extinguished all the lights on my ZHP's dash.

    Except for the "check filler cap" light, which seems to come on at random. The rub is I replaced the filler cap. I've heard the next culprit in line might be the evaporative canister in the rear of the car near the fuel tank. Before I spend another $170, I wanted to check the crowd wisdom here.

    screen-shot-2018-01-31-12.50.43-pm.png

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    RaceTape Ninja Force McCocken's Avatar
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    Chasing lights is a BMW pastime. It grates on my OCD.
    Yer pal,
    Force

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    Dammit. I just threw one of those away.

    The best way to solve all of these issues is just replace all the vacuum/breather hoses and be done with it for another 10+ years. If you don't you'll be chasing things like this forever. Replace the SAP rubber mounts as well. They are always broken it seems. While you have it apart, a cooling system refresh is in order. The M54 doesn't take well at all to overheating. These cars are now around 15-20 years old and rubber doesn't last forever.

    Did you get a bmw specific scanner yet? What codes do you have?

    Mark
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  4. #4
    Senior Member robburgoon's Avatar
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    Check for split hoses where it meets the charcoal can.

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    Indeed, "intermittently" is one of the most frustrating types of problems to track down! Although I don't have advice on a solution, I can tell you how this check is being performed - and perhaps that can lend some insight as to how you *might* be able to make the problem less intermittent.

    You are most likely experiencing a P0442 Evap Emissions Control (Small) Leak. Most OEMs will employ a test mechanism where an ambient temperature differential should cause a pressure differential in a closed system, whereas in a "system" with a leak, the pressure differential will be less than calculated. This difference - triggers the P0442. The reason is that it is intermittent is that for non-critical OBD2 codes (like the P0442), the OEM can self-clear the code if it runs the test and it is "good". In your case Brett, it does indeed look like you have a very small leak - sometimes it is being detected and sometimes it is not.

    Like others have said, I'be looking at the condition of hoses and connections and see if you can spot any signs of aging/cracking hoses and repair or replace those as you go. Another alternative is that you can go to a shop that has a smoke machine and they will pump a smoky vapor into your system and watch to see where the smoke comes out.

    Best of luck on your hunt.
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    Answer is sell bmw get faster more reliable specCorvette.

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    Quote Originally Posted by fatbillybob View Post
    Answer is sell bmw get faster more reliable specCorvette.
    That's a run on sentence. Only 2 words needed. Sell BMW
    Red_5, ucfbrett and JJ1 like this.

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    RaceTape Ninja Force McCocken's Avatar
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    Mark is on to something there and a service I am still procrastination on my wife's wagon. Systematic overhauls are the best way to get ahead on the CELs and *usually* stabilize your sanity.

    I have a spreadsheet of parts I need to order for this, I just haven't pulled the trigger. I've been trying to get my new Miata prepped for the season and reorganizing the garage so I actually have space to make these repairs. I'm dreading the phone call from her one of these days that the car is being towed because it broke. I really need to convince her how much she would like that nice, used Toyota SUV.
    Yer pal,
    Force

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    Just to emphasize what CoolTech mentioned - a smoke machine may be the only way to pinpoint the leak. All the automotive shops in my complex have one now, including me. Smoking a car is a great timesaver for things like this. I'd still replace all the hoses though

    Quote Originally Posted by CoolTech View Post
    Indeed, "intermittently" is one of the most frustrating types of problems to track down! Although I don't have advice on a solution, I can tell you how this check is being performed - and perhaps that can lend some insight as to how you *might* be able to make the problem less intermittent.

    You are most likely experiencing a P0442 Evap Emissions Control (Small) Leak. Most OEMs will employ a test mechanism where an ambient temperature differential should cause a pressure differential in a closed system, whereas in a "system" with a leak, the pressure differential will be less than calculated. This difference - triggers the P0442. The reason is that it is intermittent is that for non-critical OBD2 codes (like the P0442), the OEM can self-clear the code if it runs the test and it is "good". In your case Brett, it does indeed look like you have a very small leak - sometimes it is being detected and sometimes it is not.

    Like others have said, I'be looking at the condition of hoses and connections and see if you can spot any signs of aging/cracking hoses and repair or replace those as you go. Another alternative is that you can go to a shop that has a smoke machine and they will pump a smoky vapor into your system and watch to see where the smoke comes out.

    Best of luck on your hunt.
    Gian likes this.
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  10. #10
    Administrator ucfbrett's Avatar
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    Quote Originally Posted by markn View Post
    Dammit. I just threw one of those away.

    The best way to solve all of these issues is just replace all the vacuum/breather hoses and be done with it for another 10+ years. If you don't you'll be chasing things like this forever. Replace the SAP rubber mounts as well. They are always broken it seems. While you have it apart, a cooling system refresh is in order. The M54 doesn't take well at all to overheating. These cars are now around 15-20 years old and rubber doesn't last forever.

    Did you get a bmw specific scanner yet? What codes do you have?

    Mark
    What is a SAP rubber mount?

    The only light that came on is the "check filler cap" light. No codes. I still have my old scanner. Too broke to buy another one. I took the car to the local German shop. They had a smoke machine and I asked them to replace all the vacuum hoses and the CCV system. I know the CCV system got replaced, but I'd have little chance of telling whether they got to all the vacuum lines.

  11. #11
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    SAP = Secondary Air Pump and Mark is referring to the rubber mounts for it.

  12. #12
    BMW Master bawareca's Avatar
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    Quote Originally Posted by Force McCocken View Post


    Chasing lights is a BMW pastime. It grates on my OCD.
    I call it "Conversion to external combustion"
    Force McCocken likes this.

  13. #13
    BMW Master bawareca's Avatar
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    Quote Originally Posted by ucfbrett View Post
    What is a SAP rubber mount?

    The only light that came on is the "check filler cap" light. No codes. I still have my old scanner. Too broke to buy another one. I took the car to the local German shop. They had a smoke machine and I asked them to replace all the vacuum hoses and the CCV system. I know the CCV system got replaced, but I'd have little chance of telling whether they got to all the vacuum lines.
    A few notes from me:
    -you can never bring this car to a BMW dealer, never. I mean you can, but....
    -i have never seen a "check filler cap" light, would love to see a picture of one.
    -the most common problem with these models is the "DTML diagnostic module", which is small pump and system of valves next to the gas tank that is checking the gas tank tightness every now and then.
    -advice[s] that refer to general stuff, other OEM and so on, almost never work. You need a good scan with ISTA, the official BMW tool, is the only way to chase this, and many other problems. With this said, if you are ever coming to Sand Fernando valley you are welcome to visit the small shop that I and German guy recently opened.
    (It could be a deal for a forum sponsorship from our small venture)




  14. #14
    Administrator ucfbrett's Avatar
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    Ah, I see.

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    Brett, maybe we can make your car the basis for a nice bonfire Saturday night at Chuckwalla? For sure, that will fix the light from ever coming on again (I think).
    ucfbrett likes this.

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    bawareca has blue BMW coolant flowing in his veins. When it comes to BMW he is the man.
    robburgoon, ucfbrett and bawareca like this.

  17. #17
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    In for the partout. (Couldn’t resist)
    robburgoon and ucfbrett like this.
    Yer pal,
    Force

  18. #18
    Administrator ucfbrett's Avatar
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    Quote Originally Posted by Force McCocken View Post
    In for the partout. (Couldn’t resist)
    I'm doing a spit take over here. Now THAT's funny.

  19. #19
    BMW Master bawareca's Avatar
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    I am serious, Brad, if you want to take the care to me i will take a good look at it and give you my best advice/diagnose. It will be my pleasure to do it for you absolutely free, or a minimal fee if you insist.

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