Evap Charcoal Canister Removal & Replacement?
NEWS
 
+ Reply to Thread
Results 1 to 24 of 24
  1. #1
    Neutral
    Join Date
    Jan 2010
    Location
    Georgia
    Posts
    78

    Evap Charcoal Canister Removal & Replacement?

    I have a 2003 1.8T AWM wagon. Time to change the charcoal canister out. Anyone have experience with this and can give advice?

  2. Remove Advertisements
    VW Passat Forum
    Advertisements
     

  3. #2
    3rd Gear
    Join Date
    Sep 2002
    Location
    Yorba Linda CA USA
    Posts
    2,487
    What's the reason? I checked the hose clamps on my wagon's canister recently, looked easy enough to take out.

  4. #3
    Neutral
    Join Date
    Jan 2010
    Location
    Georgia
    Posts
    78
    Quote Originally Posted by ylwagon View Post
    What's the reason? I checked the hose clamps on my wagon's canister recently, looked easy enough to take out.
    Well where exactly is it located and will I need to be prepared for fuel spillage when I remove it. Things like that.

    I was also wondering if I need to change out the purge valve (by the air box) as well in order to make sure I remedy the "EVAP - small leak detected" code I am getting?

    Also will I need to clear the CEL or will that go away on it's own after a few driving cycles?

  5. #4
    4th Gear
    Join Date
    Apr 2005
    Location
    In his workshop
    Age
    47
    Posts
    3,886
    Blog Entries
    3
    Quote Originally Posted by chephron View Post
    I was also wondering if I need to change out the purge valve (by the air box) as well in order to make sure I remedy the "EVAP - small leak detected" code I am getting?

    Also will I need to clear the CEL or will that go away on it's own after a few driving cycles?
    The dealer will tell you that the charcoal canister and the EVAP valve need to be replaced to remedy the Small Leak Detected error code.

    The canister is $160 bucks from ECS, the valve is $60 (also from ECS). The valve replacement is 5 minutes with a screwdriver, the canister is under the trunk near the spare tire well and is no small project without a lift.

    If you haven't habitually overfilled your tank when fueling up, your canister may be fine. I had the same code for over a year, replaced my valve and reset my CEL and not seen again since except once (I reset CEL immediately and did not recur.)

    Keith

  6. #5
    Neutral
    Join Date
    Jan 2010
    Location
    Georgia
    Posts
    78
    Quote Originally Posted by keithwbloom View Post
    The dealer will tell you that the charcoal canister and the EVAP valve need to be replaced to remedy the Small Leak Detected error code.

    The canister is $160 bucks from ECS, the valve is $60 (also from ECS). The valve replacement is 5 minutes with a screwdriver, the canister is under the trunk near the spare tire well and is no small project without a lift.

    If you haven't habitually overfilled your tank when fueling up, your canister may be fine. I had the same code for over a year, replaced my valve and reset my CEL and not seen again since except once (I reset CEL immediately and did not recur.)

    Keith
    I know where to get the items, but I replaced the purge valve a couple of years ago and cleared the codes and it stayed gone. But after an SAIP issue which I believe I corrected (codes are gone) and a forced turbo replacement which threw CAT & O2 Sensor codes (which are now gone), I had this EVAP code once again. So I have cleared the codes twice and the CEL comes back. So rather than replace the newish purge valve, I am replacing the evap canister (albeit with a used one, has 100K less miles on it than mine) and trying that first. Thought I would clear the codes and see and then if that doesn't work get a new purge valve. I have also wondered if I should replace the CCV puck as well but I guess that would throw separate codes.

  7. #6
    3rd Gear
    Join Date
    Sep 2002
    Location
    Yorba Linda CA USA
    Posts
    2,487
    The canister is above a plastic cover, under your spare tire well, that is held on with three 10mm nuts. Remove those and the cover drops right off. I just picked up one corner of the car with a floor jack, put a jack stand under there for protection, and there is plenty of room to scoot under the rear bumper to get at it.

  8. #7
    1st Gear
    Join Date
    Dec 2006
    Location
    SE Michigan
    Posts
    361
    Changing your canister is unlikely to fix the "Evap - small leak detected" code. This code is tripped during the leak detection cycle when the Leak Detection Pump pressurizes your entire fuel vapor system and looks at how long it takes to lose pressure. It can either indicate a large leak (fast pressure drop) or a small leak (slow pressure drop). So the code means you have a small leak somewhere in your fuel system - it could be the fuel tank, fuel filler pipe, fuel cap, fuel vapor lines, vapor valves or carbon canister. Unless somebody performed a smoke and/or hydrocarbon sniffer test and verified the location of the leak, you cannot know which component is leaking.

  9. #8
    Neutral
    Join Date
    Jan 2010
    Location
    Georgia
    Posts
    78
    Quote Originally Posted by tallngangly View Post
    Changing your canister is unlikely to fix the "Evap - small leak detected" code. This code is tripped during the leak detection cycle when the Leak Detection Pump pressurizes your entire fuel vapor system and looks at how long it takes to lose pressure. It can either indicate a large leak (fast pressure drop) or a small leak (slow pressure drop). So the code means you have a small leak somewhere in your fuel system - it could be the fuel tank, fuel filler pipe, fuel cap, fuel vapor lines, vapor valves or carbon canister. Unless somebody performed a smoke and/or hydrocarbon sniffer test and verified the location of the leak, you cannot know which component is leaking.
    Yes I know and it may come to that, I am just eliminating a possibility with the evap canister especially with it being 177K old. Also I tend to top off all of the time and was unaware until recently that that can cause the evap canister to go bad and throw codes to the ECU. In addition, there may be a leak or crack at the evap canister or leak detection pump and I will be checking all of that while I am there. I have also already recently replaced the fuel cap and did the purge valve just 2 years ago. A smoke test is something I cannot do myself and so I am saving that for the last thing I do. I understand what you are saying though, thanks for the advice.

  10. #9
    1st Gear
    Join Date
    Dec 2006
    Location
    SE Michigan
    Posts
    361
    Maybe somebody with a vag-com can comment on this, but I would guess that you can force a leak detection cycle with a vag-com. If so, you can disconnect the carbon canister and plug/jump the lines that go to the canister and run the leak detection cycle and see if the leak goes away.

    I also wouldn't worry too much about having ruined your canister from over-filling... VW's are very hard to over-fill. If you are not going much above 3 clicks when fueling, you really shouldn't worry. If this is your concern, just remove the canister and tip it over - if any measurable amount of liquid fuel runs out then it is not going to do its job very well (but it also will not cause a leak CEL - maybe insufficient purge flow). You can also shake the canister and see if it rattles or sloshes - if not, it's probably fine.

    The canister itself should be easy to leak test if you remove it from the vehicle. Just plug all of the ports or hoses and pressurize it to less than 5 psi wth air (you can probably go to 10 psi, but 5 should get it done). Spray it down with soapy water and look for bubbles. No bubbles = no leaks = not your CEL problem.

  11. #10
    Neutral
    Join Date
    Jan 2010
    Location
    Georgia
    Posts
    78
    Quote Originally Posted by tallngangly View Post
    Maybe somebody with a vag-com can comment on this, but I would guess that you can force a leak detection cycle with a vag-com. If so, you can disconnect the carbon canister and plug/jump the lines that go to the canister and run the leak detection cycle and see if the leak goes away.

    I also wouldn't worry too much about having ruined your canister from over-filling... VW's are very hard to over-fill. If you are not going much above 3 clicks when fueling, you really shouldn't worry. If this is your concern, just remove the canister and tip it over - if any measurable amount of liquid fuel runs out then it is not going to do its job very well (but it also will not cause a leak CEL - maybe insufficient purge flow). You can also shake the canister and see if it rattles or sloshes - if not, it's probably fine.

    The canister itself should be easy to leak test if you remove it from the vehicle. Just plug all of the ports or hoses and pressurize it to less than 5 psi wth air (you can probably go to 10 psi, but 5 should get it done). Spray it down with soapy water and look for bubbles. No bubbles = no leaks = not your CEL problem.
    Thanks so much for the response, great ideas, but I had already purchased a canister and I have now installed it and cleared the codes. I also did this to check the condition of the lines going to the canister and to make sure there were not leaks at the 3 connections to it. But I am sure you are right that the canister was not the problem because I think I still have an issue. We ran a Block 071 pressure leak test of the entire evap system after I replaced the canister and it couldn't complete the test and when I ran the readiness codes for it it failed that as well. But I admit I don't know alot about resetting the DTCs on Vag Com. But no passing emissions yet. Next step is to check the purge valve again. I did the test where I tried to blow through it and I could not, indicating it is closed when the car is off which is the right status for that condition however does not guarantee proper operation (only if it were stuck open at rest would I know if it was bad for sure) so I have to do a power and resistance test on the purge valve. After that, the Bentley Leak Detection Pump test is in order and then finally a smoke test to try and figure out if any lines are bad (though they looked great at the Evap canister).

  12. #11
    1st Gear
    Join Date
    Dec 2006
    Location
    SE Michigan
    Posts
    361
    You might be able to cut down the on the number of possible leak sites if the VW engineers weren't too smart...

    The leak detection pump pressurizes the entire system, then monitors the pressure decay. "If" it only fails based on decaying to a specified pressure before a specified time, you might be able to work out from the LDP and plug various fuel vapor lines to see if the problem persists. For example, if you trace the lines from the LDP and see that it goes to the canister, then the tank/filler assembly, you might be able to plug the lines to the tank/filler (and all points ahead of this), and re-run the leak test. If you still fail for the same large leak code, then either your plugs are not tight enough or the problem lies in part of the system that was still connected. If you don't have the leak code, then you can try adding the fuel tank/filler assembly to the mix, then the vapor lines to the engine, etc. to see when you get the code again.

    The biggest potential issue with this is if the VW engineers decided to set error codes if the pressure rises too quickly when the LDP activates, signifying a blockage in the system. If they didn't do this, you should be able to use it to find the general area of the leak.

    One other thing to check before you get into all of that is to make sure the cap is not leaking - I know you got a new one, but maybe the surface of the filler screw area is damaged. If you still have your old cap, you should be able to break or cut off the plastic outer portion (where you turn it), leaving the part that seals to the filler pipe intact. Then if you screw it into the pipe you can spray a little soapy water around it and see if you get bubbles during the leak test cycle.

    Good luck.

  13. #12
    Neutral
    Join Date
    Jan 2010
    Location
    Georgia
    Posts
    78
    Quote Originally Posted by tallngangly View Post
    You might be able to cut down the on the number of possible leak sites if the VW engineers weren't too smart...

    The leak detection pump pressurizes the entire system, then monitors the pressure decay. "If" it only fails based on decaying to a specified pressure before a specified time, you might be able to work out from the LDP and plug various fuel vapor lines to see if the problem persists. For example, if you trace the lines from the LDP and see that it goes to the canister, then the tank/filler assembly, you might be able to plug the lines to the tank/filler (and all points ahead of this), and re-run the leak test. If you still fail for the same large leak code, then either your plugs are not tight enough or the problem lies in part of the system that was still connected. If you don't have the leak code, then you can try adding the fuel tank/filler assembly to the mix, then the vapor lines to the engine, etc. to see when you get the code again.


    The biggest potential issue with this is if the VW engineers decided to set error codes if the pressure rises too quickly when the LDP activates, signifying a blockage in the system. If they didn't do this, you should be able to use it to find the general area of the leak.

    One other thing to check before you get into all of that is to make sure the cap is not leaking - I know you got a new one, but maybe the surface of the filler screw area is damaged. If you still have your old cap, you should be able to break or cut off the plastic outer portion (where you turn it), leaving the part that seals to the filler pipe intact. Then if you screw it into the pipe you can spray a little soapy water around it and see if you get bubbles during the leak test cycle.

    Good luck.
    Thanks! That's a good idea on the fuel cap, I did not think of that. I have just put the old fuel cap back on and I am going to re-try the Vag com pressure test first before I cut up one of the fuel caps, but that may be the next step. The other possible culprit according to the Vag com codes is the Evap canister purge solenoid which I have been unable to locate. Any ideas? By the way, I have never gotten the large leak detected code so I was advised that it wasn't likely that it was the line that runs on top of the fuel tank which I presume goes to the breather vent. But I don't know. All I can say is that I was surprised by the rapid fire sound of the LDP when I forced the pressure test, but then I have no idea how it is supposed to sound.

  14. #13
    3rd Gear
    Join Date
    Sep 2002
    Location
    Yorba Linda CA USA
    Posts
    2,487
    Quote Originally Posted by chephron View Post
    All I can say is that I was surprised by the rapid fire sound of the LDP when I forced the pressure test, but then I have no idea how it is supposed to sound.
    How exactly did you force that test? I've got the full-access VAG-COM but haven't tried that one.

  15. #14
    1st Gear
    Join Date
    Dec 2006
    Location
    SE Michigan
    Posts
    361
    Somehow I forgot you had a "small" leak code and thought it was a "large" leak. Small leaks are much harder to locate than large ones - they can be as small as 0.5 mm in size. The purge solenoid you are looking for is just another name for the purge valve near the air cleaner. It's possible that VW forces the purge valve/solenoid shut during the leak test and if it is partially open it could show as a leak (but that's just a guess). You could test this by removing the purge valve and plugging the hose. If you still get the leak code, the purge valve is not the problem.

  16. #15
    Neutral
    Join Date
    Jan 2010
    Location
    Georgia
    Posts
    78
    Quote Originally Posted by tallngangly View Post
    Somehow I forgot you had a "small" leak code and thought it was a "large" leak. Small leaks are much harder to locate than large ones - they can be as small as 0.5 mm in size. The purge solenoid you are looking for is just another name for the purge valve near the air cleaner. It's possible that VW forces the purge valve/solenoid shut during the leak test and if it is partially open it could show as a leak (but that's just a guess). You could test this by removing the purge valve and plugging the hose. If you still get the leak code, the purge valve is not the problem.
    Ok that is a good idea. Just got to make sure the plugs are sealed right. But as far as the purge regulator valve being the same as the purge solenoid valve. They definitely are not, purge valve is a N80 and the purge solenoid a N115 and are listed separately by the Vag Com on the 16825/P0441 Evap code.
    The N115 doesn't appear to near the air box, unless I am missing something.

  17. #16
    Neutral
    Join Date
    Jan 2010
    Location
    Georgia
    Posts
    78
    Quote Originally Posted by ylwagon View Post
    How exactly did you force that test? I've got the full-access VAG-COM but haven't tried that one.
    Well from the Vag com home screen, you have to click the basic settings button first and then type in 071 in the left hand most field labelled "block". Then you simply follow the instructions below. Pretty simple really.

  18. #17
    Neutral
    Join Date
    Jan 2010
    Location
    Georgia
    Posts
    78
    Ok so now I have tested with the old gas cap and newer evap canister and still failing the pressure test for the LDP system. I think I am gonna replace the purge valve since I can get it pretty cheaply to eliminate the last variable (well besides an LDP) before I do a full LDP test by incrementally plugging lines and pressure testing. And if that doesn't work, I suppose it's time to take to someone to smoke test it out.

  19. #18
    Neutral
    Join Date
    Jan 2010
    Location
    Georgia
    Posts
    78
    Well I had a chance to test voltage and resistance on the LDP and they were fine along with all of it's hoses. Pulled a vac on one of them, no problem.

  20. #19
    Neutral
    Join Date
    Jan 2010
    Location
    Georgia
    Posts
    78
    Now I have tested with a brand new fuel cap from the dealer and still have the Very Small Leak Detected and so I have ordered a Purge Valve (N80) and will try the LDP check one more time before having a smoke test done. As a side note, I had performed a block 070 test to check the evap canister itself and it passed. So I am thinking the purge valve is the last thing to verify before smoke testing and replacing lines and/or the bleeder valve off of the fuel fill neck.

  21. #20
    1st Gear
    Join Date
    Dec 2006
    Location
    SE Michigan
    Posts
    361
    ...or you could live with the check engine light. A small evap leak is unlikely to affect vehicle function. Twenty (OK, thirty) years ago you would never have known there was a "problem".

  22. #21
    Neutral
    Join Date
    Jan 2010
    Location
    Georgia
    Posts
    78
    Quote Originally Posted by tallngangly View Post
    ...or you could live with the check engine light. A small evap leak is unlikely to affect vehicle function. Twenty (OK, thirty) years ago you would never have known there was a "problem".
    That would be great, except we have to pass emissions where I live. And mine is coming up in 13 days!

  23. #22
    Neutral
    Join Date
    Sep 2011
    Location
    fort lauderdale, FL
    Posts
    43
    Just a note ++ Please keep us Passat World members ,,how this resovled,,just love to learn how things work out,,common fixes or info,,in other words dont leave us hanging ,,ouch,,lol ,if you find the fix ,please inform us members thanks

  24. #23
    Neutral
    Join Date
    Jan 2010
    Location
    Georgia
    Posts
    78
    Quote Originally Posted by fortlauderdale View Post
    Just a note ++ Please keep us Passat World members ,,how this resovled,,just love to learn how things work out,,common fixes or info,,in other words dont leave us hanging ,,ouch,,lol ,if you find the fix ,please inform us members thanks
    You got it. I was planning on it, I am sure I will be something of an expert once this is all over. Purge Valve is on the way, would have started with that but had just changed that out 2 years ago and it seemed fine on a simple test but it's now the next best thing to try.

  25. #24
    Neutral
    Join Date
    Jan 2010
    Location
    Georgia
    Posts
    78

    EVAP 16840/P0456 issue solved!

    Thanks everyone for the advice and responses. After much troubleshooting it ended being that the purge valve was indeed the culprit. As soon as I replaced it, the code went away and I have now passed emissions! One thing I should note though, that the evap canister (which I replaced) if it went bad, could definitely have caused my purge valve to fail prematurely and so I am glad I fully diagnosed the whole system instead of just changing the purge valve out.
    Also a wise guru told me to put a generic fuel filter in line between the evap canister and the purge valve to prevent future clogging of the valve. I think I might take him up on that idea if it doesn't cause any CELs.

    Anyway , problem solved. Hope this troubleshooting helps someone else as well.

  26. Remove Advertisements
    VW Passat Forum
    Advertisements
     

Thread Information

Users Browsing this Thread

There are currently 2 users browsing this thread. (0 members and 2 guests)

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
Powered by vBadvanced CMPS v4.1.2