S8ilver

So I had P0442 a few years ago...turned out to be a loose gas cap.

I had it again about 2 months ago, replaced all vacuum lines, and yet it continued. I replaced the vapor canister purge valve and code went away...

...for about a month of consistent driving. This morning, CEL and another P0442 "small evap leak detected."

New cap/o-ring at sending unit? I don't smell any fuel.

https://www.audiworld.com/forums/sho...ighlight=P0442

http://genuineaudiparts.com/parts/in...&siteid=214407

What do I search for next??? Keep in mind I only replaced the vacuum lines per:

http://www.audipages.com/Tech_Articl...sereplace.html

Should I do all the others? I have plenty of 3, 4, and 5mm silicon hose to get the right fit everywhere. I know the code doesn't really affect drivability, but it's affecting my sanity.

S8ilver

No advice? I'm at the guessing stage, and evap components only get more expensive beyond the 2 I've replaced. I guess I'll buy a new gas cap, even though original seems to function perfectly (and passed emissions leak test).

Smoke test?

silverd2

If it's not the gas cap (probably not with a new one), there a lot of other components and hoses involved:

- Leak detection pump in the left rear fender well, that generates the pressure for the test that sets off the code...reads and times the leak down after pressurizing the evap system.

- Evap canister under the car (under spare tire well) with it's hoses.

- Fuel filler neck with it's expansion tank, in right rear fender well and it's vent hoses and vent valve.

The only time I've had the code with my D2, I cured it by cleaning (and rubber treatment)the gas cap gasket and double checking it's tightness every time.

My wife gets that code with her Allroad and while doing a quick check (no repair yet), i found the evap canister half full of gasoline...likely the previous owner (and her?) overfilling the tank (topping off), which lets gas pour down the vet hose...this likely has lots to do with the code...we'll see.

Below is a chart from Bentley...the parameters are interesting, like elevation (although 2600...not quite "mile high") and leak detection pump working properly...The LDP is supposed to generate it's own failure codes, but it has hoses that have to be sealed and even it's own changeable intake filter.

That's all I got...hope it helps.

PS.. I don't have the full version, but there are VagCom test for evap leaks, including LDP tests.

S8ilver

Thanks so much.

I'm under 2600m, at least when I'm in the city. Each time the code's gone off, I've been in or around Denver. I just find it odd that it didn't come back for a month after I replaced the purge valve. Heck, maybe a vacuum line I replaced popped off.

I'll inspect a bit more this weekend. I just hate throwing $ at things that may or may not be bad. The vacuum lines were due, so that's fine. Purge valve was ~$40. I'll swap out the rest of the vacuum line on front of the motor for good measure.

I've cleaned the cap as well, never overfill, and always give it 2-3 clicks when closing. I guess a new gas cap won't hurt though.

Is evap canister accessible thru trunk, or just from underneath? On which side of spare tire well?

What about a bad PCV? Would a sticky PCV throw the same code?

silverd2

The evap canister is directly below the spare tire well, under the car...3 bolts on big round panel.

Most vacuum lines on the front of the motor would have no effect on the Evap system, which is only for gas vapor ventilation/fuel tank sealed system. The same is true of the PCV valve and hoses...that's just crankcase oil vapor. Problems with front vacuum lines or PCV would likely throw different codes and/or lead to different system failures (therefore codes), like secondary air injection...nothing to do with evap.

The leak detection pump can be gotten to by simply removing the left rear fender liner...like I said, it's the main part of the evap system. When you first start the car, it runs to pressurize the vapor side of the fuel system..fuel tank, canister, etc.. Then it times/measures the pressure for a couple of minutes after the test.

Y888

Just wanted to say that i fixed a problem where i couldnt fill up my gas tank at the station.
Pump would constantly cut off so i replaced purge canister valve(parts geek bosch 35$).
And now its all good.
Its smaller than oem and doesnt have that slot for holder but it fixed my problem.

edit:im dumb its same as oem and has a rubber holder that goes around it

jfrahm

I have chased this a bit on my 2001 A8. I replaced the gas cap, code came back. Replaced the N80 purge valve, code stayed away for 8 weeks but then came back. Since then I have been careful filling up the car, not topping off, as I recall it has thrown the code after a fillup. So far no code, it has been at least 8 weeks and a long trip with many fillups. Nowadays I just stop filling the tank after the pump clicks off. I am not sure if my code is due to an issue perhaps in the evap system, or maybe there is a tiny leak but if the gas tank is not super full the leak detection system is buffered by the extra volume of vapor causing a much slower change in the vacuum during the test phase. Obviously if the tank is low on gas it'd be a heck of a job for the leak detection pump to pull down enough vacuum to see much of a change and throw that code.

It is good to eliminate the gas cap. The Stant gas cap is under $5 and I also found a Volvo seal (volvo part 940096) for the gas cap (or oil filler) that fit the OEM Audi cap pretty well. Also I learned to my dismay that Colorado will now fail your smog test if your gas cap does not seal on their testing machine so it's a really good idea to have a good or new gas cap on there so you do not have to come back and wait in line again due to a few cracks in your gas cap seal. I bought an S8 and needed to smog it, had a new cap on the A8 but the OEM cap on the S8, and the cap failed the test (no codes though). In general I prefer the stock cap so I tracked down that seal.

Matthew Chandler

so after reading these (and many other forums) searching for the answer to my small/large evap leak CEL codes, I finally caved and brought my car to a shop to have a smoke test done. In hindsight I could have used a DIY homemade cheap smoke tester to find this issue. I highly recommend giving that a shot at least before shelling out $100 for a 5 minute test.

On to the findings: as soon as the tech hooked up the smoke machine to my gas fill neck with an adapter smoke started coming out from around the full neck, from underneath the wheel well. Turns out the full neck has two expansion chambers and each of those chambers has a breather hose connected to either the charcoal canister or the gas tank itself. Both of the connections come out of the expansion chambers, through the metal behind the wheel well and towards their destinations. On the other side of the metal there is maybe 3 inches of the solid opaque/yellow plastic tubing. Just so happens the line going to the gas tank right here has a massive crack. It was clearly a series of small cracks that developed into a serious hole. Completely explains the evap systems inability to pressurize the tank and the related engine codes. Not sure yet what I am going to do about it yet it I am looking forward to the challenge.

As as it turns out the filler neck and expansion chambers are all part of the gas tank assembly, not sold separately, not able to be disassembled in any way. So now I have a crack in a plastic tube that I can't replace and lots of other brittle plastic around it to be careful of. I am hoping some sort of tape, or epoxy will hold it sealed. I am also thinking of removing the rubber hose connected to this plastic garbage and seeing if I can feed more rubber tubing into the plastic junk to create a better pathway. Not sure how that will fair yet.

Any my other ideas would be appreciated. If I can manage I will try to post pics of what I am working with.

Matthew Chandler

Now obviously it wasn't like This the first time I went and looked in this area. Must have been just cracked while I was messing with the N80, which ended up needing to be replaced. Dang, should have gotten a picture of my Jerry-rig. Basically I shoved a piece of tubing into the bottom of the expansion tank and the other end I slid inside the larger tube that was already there. One side has a hose clamp and will likely hold, but the other is still just jammed up in there. That side will need to be changed. I was just looking for something for now until I can get something better.
FYI that picture is rotated 90 degrees ccw for some reason.

jfrahm

After my last post in this thread I found cracks in my fuel pump cover and goobed them up with RTV, this was mentioned over in the QW D2 forums and found to be a common problem. I think not topping my tank off was masking the P0442 codes. I have been code free for a long time since the RTV effort but I still do not top off my tank.

Thanks for pointing out this other area that can cause the small leaks.