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Discussion Starter #1 (Edited)
P0456 - Small leak detected - Not N80 valve - FIXED

Hi,

My 02 1.8T got a CEL. Scanned it and showed P0456. Replaced the gas cap with one from Autozone. Still CEL came on. Removed and checked the N80 (purge valve) and it was slightly leaking (i can suck from the vacuum side without applying 12 V). Replaced with a new one and also replaced the check valve next to it (which was also slightly leaking). Did the vag com test with block 071 and still got error saying slight leak.

Went under the car and removed the 2 hoses from canister. One goes to engine side (N80) and other goes to tank. Tried to blow through each with mouth and N80, it was fine, but tank one, cant say for sure. It needs to fill up the tank i guess. Took some time to make it under pressure. Then connected the hose to the engine back to the canister and put my finger on the canister where the other hose connects. Now re-ran the test and it passed. So it confirmed that the Leak detection pump, its hose, canister, the hose to N80 valve and the N80 valve is fine. The fine leak is some where in the fuel tank area.

Next i tried to blow air to the hose which connects to the tank. Once the maximum pressure is reached, i closed it with my finger and tried to listen for leaks. Cant find any. Since engine was not running and it was a quiet area, it should have been easy to hear. I removed the fuel door mechanism and used a mechanical stethoscope to check for air noise around the bleeder valve / gravity tank. No sound at all. After all this tests like 5 minutes, when i opened the hose again, it had air in it. I mean it was still pressurized.

Now i am completely clueless. Any idea? Only smoke test can reveal it? Also planning to get an OEM gas cap and try again. Autozone gas cap clearly looks different.

Thanks in advance..
 

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Discussion Starter #2 (Edited)
Replaced the gas cap with the one from dealer. As expected, it did not fix the issue.

Planning to do as below
1) Some where i read that a bad PCV can cause issues (only on VW). Open the oil cap while engine is running and see if too much vacuum.
2) Remove the breather valve which connects to the canister. It have some O-Rings. They might be aged. Check it and see. It got 3 connections. One goes to the fuel tank (close to filler neck), second one goes to the hose which goes to canister and third one goes to the gravity valve. Also planning to do some test without inserting it back. To rule out gravity valve and this valve it self are not leaking..
3) Check the fuel pump area and see if any visible air sound. Planning to pump air into the tank via the hose from the canister (with mouth).
4) The FPR, check and see if it have some issues. Need to find out more information on how to do it.
5) Clean the LDP filter and when it is running make sure that no air leaks via the air filter area.

If all turns out good, only thing left is the smoke test.

I will update once i found out something.
 

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It's not clear whether you looked at the vacuum piping and check valves on the drivers side under the intake. On my 03 there are two check valves and a mess of piping and fittings over there that connect to the evap sys. Follow the hard pipe across the engine bay between the purge valve and the vacuum reservoir and you should be able to find them.
 

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Discussion Starter #4
Thanks uberbeagle.

I found that there are three connections with a check valve to the EVAP system.

1) To LDP pump from intake manifold
2) To N80 value from intake manifold. It is basically one line coming from intake and 2 check valves are routed, one to N80 and one to LDP
3) From N80 valve to some other place which goes under air intake. There is also a check valve.

Since my N80 valve is new, it cant leak (i tested it also). Also when i did the test, if no fuel tank hose connected, the test passes. So it is some where in the fuel tank area.
 

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Upon carefully re-reading your post, I do see now you were testing on the drivers side. I saw the word canister and my mind immediately jumped to charcoal canister when you actually meant the vacuum reservoir canister.
Problem must be in the back then as you say. I've never had any problems back there so can't be much help. I will be curious to know what the problem was when you do find it.
 

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If your back there looking for a leak and can get your hands on a Vag-com, you can initiate a test of the evap system I believe. Then you could repeat the test, clamping shut lines working your way away along until you get a pass to narrow it down. You could also try a fuel leak tester if you can find one to borrow.
 

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when i did the test, if no fuel tank hose connected, the test passes. So it is some where in the fuel tank area.
I didn't follow that. Which fuel tank hoses do you mean? Was the LDP isolated (testing itself) or what? It's worth using soapy water on the fuel tank access port where the electrical connector and fuel hoses attach. Also, my B6 A4 had a small leak that I couldn't track down. Eventually my son-in-law learned that damage to the plastic lines in the wheel well (LDP area) were common due to rocks, etc.

As a point of interest, the LDP is powered by engine vacuum, not electicity. The electrical connector is for the solenoid valve and switch contacts, and can't make the LDP run if vacuum is not available.
 

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Discussion Starter #9
I was using VAG-COM to do the testing. Block 71.

ylwagon - I was referring to the hose which connects from the charcoal canister to the fuel tank. I did a test (VAGCOM) with this hose disconnected at canister side and covered the port at the canister with my finger and ran the test. It passed. So i think i isolated it to the fuel tank area. At this point of testing, the LDP was pumping ( i can hear and i can feel the air pressure in the finger) and there was no leak in canister area. Since the test passed, i guess the vacuum, LDP, its hoses all should be fine? Also the canister.

fuel tank access port? Where is that ? Also the plastic lines in the wheel well, is that the vacuum line/ hose to canister from the LDP? Or any additional lines?
 

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Discussion Starter #10
Removed the fuel pump cover and checked it. It was really dirty and cleaned it. With a stethoscope it is impossible to hear any leak sound during testing (the pump makes noise). So i guess soap water?

Also checked the breather valve area. I can turn it by hand (it have some O-Rings in it). If easy, i am planning to take it out and re-do the test. If it passes, then the leak is in the tank / pump area. Otherwise, it is the value or Gravity valve/tank.
 

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The difference between "small leak" and "large leak" fault code is a matter of how long it takes for a set of contacts to close in the LDP, after it has pumped up the pressure. The small leak might be so subtle that you won't hear it, something like a tire leak that you can't hear, but makes a foam of bubbles when soapy water is over the spot. I would start with that fuel pump cover, using the soap solution. After you are done, disconnect the electrical connector and make sure all contacts are dry before reconnecting.
 

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I'd probably brush it on using a paint brush, using dishwashing soap with water. You don't want to start off with a lot of bubbles from a sprayer.
 

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Discussion Starter #14
Thanks..Will do it and update.

I guess the best option is to remove the hose at the canister side (which goes to fuel tank), blow air to pressurize it, cap it and then do this soap trick should show it.

The vag com test, it finishes pretty soon. I have to go back and do it again and again. So thought of doing like this. It holds the pressure for a while.
 

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Discussion Starter #15
Tried the soap at the fuel pump area. No leak at all. When the test was running, i did this. No bubbles at all.

Removed the LDP, cleaned its filter. Ran the test while it was out. It is pumping nice. Kind of like cycle pump way. Again confirmed that when i cap the port at canister which goes to fuel tank, it is passing the test.

I just checked the air pressure coming out of the canister. It is ok, i was expecting a big push, but not that much. Kind of like whoosh push.

Now it all points to the either the tank it self / breather valve/ gravity valve etc. Planning to take it to a shop and do a smoke test. Tired of doing this.
 

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Discussion Starter #16
I was wondering if i can just replace the fuel pump gasket to see if it fixes it. Since it is rubber, high chance that it can fail with age? Also the O-Rings in the breather valve

Other areas, there are more than i thought. There is a fused kind of thing which goes to the gravity valve from the fuel tank, then hose from breather valve and so on.

Its true, only a smoke machine can show it properly. With so many connections from tank.
 

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take the car to a dealer, and have them put it on a smoke-machine...

this would easily be worth the $128 our dealer charges for diag, JUST so i wouldn't have to fumble through evap systems...
they can be a horrible pain to diag without the right machines/tools. smoke machines are magical for this reason.

"oh! look! smoke... it came from here!... that must be my problem."
 

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Discussion Starter #18
Already talked to one shop in Plano and taking it there tomorrow. They charge $75 for smoke test. One of my friend had taken his car there sometime back and they were really good.

Somehow i never had good luck with the dealership. Last time, the PCV system, they misdiagnosed it was oil pan gasket and total estimate was for $4.5K which was more than the worth of the car.

Will update once the smoke test is done.

Just to be curious, does some one else had this same issue and how it was resolved? What ever i read, almost all of them were N80 valve. No one had fuel pump seal leak/gravity valve leak/tank leak.
 

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what shop is it?
i'm an advisor in the mckinney store. contact me (through pm) if you need anything :)

btw, i'm very happy to say that we have the old boardwalk foreman with 37 years vw, as well as the literal vw #1 national rated technician. (#2 world)

i love where i work.
 

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Discussion Starter #20
It is called AAA auto repair. I've been there multiple times with my friend. One time cam sensor, next fuel pump and so on. So called and took an appointment.

So you work at the McKinney VW? I've been there (to buy the pollen filter housing)
 
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