john981

Few weeks ago I had my check engine light coming up with this code p0456: very small evap leak. I brought the car to my indy and he rested the CEL and told me to try a new gas tank cap and see how it goes. After the reset and the new gas cap, I haven driven the car for over 1000 miles. No CEL at all BUT, when I put my code reader (Icarsoft v2) on, in the general mode (not car specific mode) from time to time this code comes back on. It is very strange because sometimes the code is coming up and another time when I run the machine there is no code at all. The CEL has never showed up again. Anyone an idea what it could be? Thank you in advance for your help.

LexVan

Charcoal canister for the fuel tank? Do you often fill beyond the automatic shut-off??

john981

Yes I do. Any suggestions what I should do?

LexVan

Well, for starters, STOP over filling your tank beyond the automatic shut-off. That's killing your charcoal canister. How you rectify that is past my pay grade. Sorry. But I feel this is the root cause and gives you a reference point to go back to a skilled mechanic. Are you out of warranty?

john981

Will do, didn't konw about the over filling issue, thanks for the advise. Yes, my car is out of regular warranty but I have still the emission warranty in california which covers all parts of the emission system. I have hooked up my icarsoft again yesterday while the engine was still cold and there was no code again!? There is really no clear pattern when the code shows up but when it shows up I don't see anything with the CEL.

I called several Porsche dealerships and they all told me as long as the CEL is not on, there is no need to bring them the car- without the CEL, they might not find anything and I would waste my money on diagnostics. By reading around, even with the code permanently on I am safe to drive, it is just annoying to know something is wrong with your car.

Jack F

In a VW Jetta that my wife had years ago, it had 2 codes that were tracked down to a valve under that would open as needed to let the tank vapors end up in the engine I guess. It was stuck closed if I remember correctly and changing out hot part sorted it out. Maybe it is something in the chain that is misbehaving?

john981

This very small leak code is pretty tricky. It can be anywhere in the entire EVAP system. I guess I will wait until the CEL comes up again and will just bring the car to the dealership. I think I can afford the 250 for the diagnostic :-) If I am lucky it will be covered under the emission warranty. If not I will just take it to my indy. I hope with the CEL permantly on they can detect the issue more likely than with the situation I have know where the code comes and goes. I was just wondering if anyone else had seen this kind of issues but I guess I am the only paranoid person here who hooks up his code reader twice per week to see if his car is fine :-)

Jack F

Dealer will likely have seen this before. If the tech has not hopefully they talk with the other techs. I might be cheaper I the end through the dealership since they experience amongst the techs should be substantial. If they talk with one another though.

DHL

I believe this code is sourced from a pump down (or pressurization) of the fuel tank and connections. The car measures the time to leak down and it must be longer than a particular period of time to pass. If you are right on the edge, some tests you may be passing while others you may fail. In some systems, you may have to fail more than once or twice to have the Check Engine light activated. But it still may throw an "active monitor" without the CE light. This active monitor may be what your scanner is picking up. Also, most of these monitors are automatically reset after a certain number of driving cycles are completed without the fault being repeated.

john981

Thank you, it makes sense. do you have a suggestion what I can do here?

DHL

Well, since the new gas cap helped, there may be other components like hoses that may also be cracked or leaking. But this is a 991, right? Kind of new to be having these problems. Only real solution is to go over the evap control system and look for loose, cracked hoses or fittings. May also be the pump but I have no idea where that is or how to test it. And stop overfilling your gas tank.

Chris C.

Hello all - another mention for this code, and it did follow (by a week) me going beyond the auto-shut off on a fill up.

Gas cap is on tight and it is in the "upgraded" fake stainless version from Porsche so it has to be solid, right?? . I've reset the Fault ...let's see if it recurs ...

Car was out of warranty in Nov but as others noted emissions covered for 10 years I believe in CA.

OP - did you resolve your issue? Has anyone had a dealer address?

Porsche_nuts

I have gone past the auto shutoff many many times and have not had any codes.

MY 2015 GTS

koala

Just a matter of time before you do. This is not a good habit on any modern vehicle!