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Discussion Starter #21
Update: Talked to the shop and they said they could not duplicate and it passed the inspection. Also no CEL and he said car is ready to go.
 

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Discussion Starter #22
The CEL came again. This time it is P0442. So it changed from fine leak to small leak. It is increasing..

Removed the hose at the canister which goes to the fuel tank. Connected a cycle pump to it and pumped it. I can hear the leak. Opened at the fuel filling area. Removed the fuel door etc and the leak is very easy to hear. Sprayed the soapy water and found one place which is making bubble. It is on the left side, where the breather valve connects. Removed it and lubed the multiple O-Rings with oil and put it back. Still the same. Planning to replace it and try it again.

Will update after replacing it. It is a pain to replace it. One clamp, the one goes to the tank, is almost unreachable. Need to drop the tank to do it properly :(
 

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Make sure you take some pics so others can see what needs to be done.
 

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Discussion Starter #24 (Edited)
Sure..will do it PZ. Ordered the part online. Hopefully it will fix at least this leak.

Part number is 4B0201736A. This is what is bought VW Volkswagen 01 05 Passat 2 8L V6 Fuel System Valve 4B0201736A | eBay. It seems those O-Rings are week. The bubbles coming out was big in size, but the air noise i can hear, was much bigger. Once this is replaced and that leak is fixed, then i can chase if any other is present.

Dropping the tank is the best method to fix this. I really hope i don't have to do that.

This is the valve..mine is not separated like his.

http://www.passatworld.com/forums/volkswagen-passat-b5-discussion/299906-large-evap-leak-ands-not-gas-cap.html#post2428594
 

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I thought the shop was pretty lame not to find the leak just because the CEL was not on. They should have run the smoke test anyway. That is a rather weird looking valve, not sure why it would need 3 sets of O-rings.
 

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Discussion Starter #26
I was trying to find how it works. It is called "Tank Bleeder valve" ( i think so).

Out of 3 connections on this,

1 - Goes to Canister
2 - Goes to fuel tank (the small connector)
3 - Goes to side of the fuel filler area.

From what i understand,

3 gets vapors from the fuel filler area(when filling) and also from the gravity valve (when gas cap is closed) via the hose goes on top of the fuel filler. It will routed to 1 via this valve
2 gets vapors directly from the tank - A picture from ECSTuning website.
 

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Discussion Starter #27 (Edited)
Finally i was able to change the bleeder valve. Item # 4B0201736A (the white color valve in my previous post). Tested with VAG-COM and this time it passed. I really wish it was this one. So far i changed the fuel cap, the N80 valve and this one.

The diagram. I drew it based on my finding. May be missing / wrong in some areas
Diagram.jpg

To replace this, if the tank is dropped, it is damn easy. Without that, it is a pain. Here is what i did

1) Remove the TorX screw (T -15 i think) and remove the fuel door mechanism
IMG_3096.jpg

2) Now it will look like this
Fuel Door Removed.jpg

3) Press on the highlighted area and remove the latch mechanism also. Now you can clearly see the valve
Valve 1.jpg

4) Removal is tricky. The big connector, as you can see, i have worm clamp. It was originally the VW *.* clamp. Cut it with dremel tool / big cutting plier. Insert a flat head screw driver between the valve and the hose. Then pry it down.
5) Now remove the valve it self. Insert a small flat head at the notch area and pull it out. Remember, at this time, the hose on the side, is still connected.

IMG_3102.jpg

6) Now the hardest part. Press it down and cut the clamp with dremel tool. After that insert a flat head screw driver between valve and hose and pull it out. Be careful, don't pull hard, the hose may get disconnected from the tank.

7) Put the new one in, first attach the side hose, insert it into the fuel filling area, make sure it is locked, then connect the big hose.


Now you can use VAG COM block 71 to test and see if all is right (engine should be running to do this test).


Just a recap, all this was to fix the P0456 (fine leak) which turned to P0442 (small leak). If any doubt, please ask and i can answer what ever i know.
 

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Got this same issue, only happens when i'm under half a tank and it's cold in the mornings. Going to get a new bleeder and try to swap it, thanks for the investigation Saneeshd.
 

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Bump up for old thread! For info, using the details from Sanesheed, i removed the tank bleeder valve, removed and regreased the rubber o rings and the orange end seal (with thick silicone grease - 50000 CST from local hobby shop).

Fitted the valve back in and waited for the next 'trigger' event (cold engine - overnight, low gas quantity). I guess the test must have parameters when it is run and low gas quantity seems to make the leak more easy to detect (more ullage to maintain vacuum on?)

Anyway, i've not had a 'check gas cap' with associated P0456 ever since. Worth a look.
 

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I'm having the same problem and thanks to the info in this post I've tracked it down to something in the tank area. As mentioned above, I ran the Basic Settings test in VCDS group 71 to test the EVAP system and it failed until I plugged the (larger) output from the charcoal canister that is open in this picture. I assume that it is the line going to the tank spout area so please let me know if that's not correct.

Interestingly, my car only throws the CEL when the tank is nearly full. I don't know why so I'll probably drop the tank when I get a chance and go from there.

98381
 

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This plastic lines are known to crack over time from debris or flexing. As a troubleshoot, wrap in vinyl tape or coat them somehow to see if it keeps it from triggering a code for a leak. Absent that, try a new fuel cap. Second thought, try the cap first.


Sent from my iPhone using Tapatalk
 

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My A4 had similar small leak, in that case a rock likely got thrown against the fender liner, damaging the tube right behind it. That was tough to figure out, until an Audi tech suggested that to my son-in-law.
 

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I've tried two caps, both from pick-n-pulls but they looked newish and appeared to be fine. I'm thinking I'll try a new rubber o-ring on the gas cap and then check the lines behind the fender liner. It looks like dropping the tank on a FWD wagon isn't that hard but I'll probably try it in a junkyard first to see if I really want to do that.
 

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That looks to be the vapor line to the filler neck, like you said.
 
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