P0456 - Very Small Leak

[canonball]

Ok guys, I got a CEL the other day, scanned and got a code for this evap leak. I did some searching around but haven't seen much in the way of helpful results. Would a VCDS scan tell me any more details on where to look for the source of the problem? I'm trying to avoid just throwing parts at it, if possible. Would a smoke test in the evap lines reveal the issue? I've done some snooping around under the hood already and haven't seen anything. N80, PCV, gas cap were all things I saw other people were told to check. Any thoughts? This is on my '05 A4 1.8t 6 speed.


Car Scanner ELM OBD2
Version: 1.97.4/1.97.4/iOS
DTC report
Connection profile: Audi OBD-II / EOBDDate: 3/24/2023 6:04:09 AM
VIN: WAULC68E95A033312
============================
OBD-IIOBD-II
DTCs: 1
----------------------------
P0456 [0x0456]
Evaporative emission (EVAP) system - very small leak detected
Status: Confirmed

[Mike Tries]

I might have this code now. It is a "very small leak detected" code, at least. I tried a new gas cap, to no avail. The error happens for me when the tank is near the 1/4 mark or below. Does yours do the same? I suspect for mine that the filler neck is cracked. It never occurred to me to... you know... actually find out what's wrong first. If I remember to, I'll hook up to VCDS tomorrow and see what it says (and see whether it's even the same code).

Edit, for clarity, I suspected the filler neck because I was led to believe a gas cap would fix it. (Does the car suggest this somehow? Or maybe the scanner app? Whatever. Haha.) Anyway, if it wasn't the gas cap, what else could be in the vicinity? The filler neck itself. And... somewhere around where the 1/4 tank level would sit in it was my guess.

[canonball]

Hmm, I'm trying to think, when the CEL first reared it's head I think I was on the lower end of the gas tank level, but I'm not 100% on that. I have filled it since and the light is still there. Not sure if the code needs to be cleared manually but I would assume it would clear itself once it had a chance to run through it's cycles which with my commute it would certainly have that chance since I filled up so in my case I'm leaning towards something else. But that is a very good point and I'll definitely keep an eye on my fuel level while I'm troubleshooting this issue.

The other threads I found with this P0456 code seemed very messy, the code itself doesn't seem to tell you much (from what I found), so it leaves a lot a guess work and half the threads had no resolution, OPs just went MIA at some point before reporting back about findings or whatever. Somebody must have a little more solid idea about the cause. I feel like if I can track someone down with a smoke machine that I could hook up to the evap system then I would think that would help pinpoint any leaks and should clear the code.

I'll try to keep this thread updated for any other future peoples with this issue.

[Cybersombosis]

N80 valve? And yes clear the code and see if it comes back first.

[kwilson]

I have seen this code before. I was able to clear it and it never came back. Hope you are as fortunate.

[Mike Tries]

Yeah, I've got that code, too. Scanned it in VCDS. It doesn't really say more than you got from your scanner. If anybody has some ideas about how I may be of more help with this issue in VCDS, I'd be happy to help a bit more!

Also of note, see all those open circuits on all four ignition coils? Probably evidence of the exposed wiring shorting in there.

Edit, no, duh.... open circuit is from when I had them unplugged and cranked the engine. Disregard. Haha.

[RPMtech147]

If you can't perform a valid smoke test of the evap system, your only option is to start chucking parts. Purge valve, LDP, lines, etc, etc. I see a lot of fuel tank modules (the pump cap/filter/sender unit that sit on top of the tank) leak pretty often... The tiny leaks are hard to find. Even with a smoke test. A lot of times I have to do a smoke test, with soap/water to get bubbles...

Spend the $150 and have a Euro shop that knows what they're doing, diag it. Then do the repair yourself. If no leak is found (Flow gauge zeros, no physical leak) replace the purge and the vent (LDP).

Sounds like you already replaced the cap.