a couple weeks ago I filled up my car for the first time this year, pulled out of the gas station and got the "check gas cap" alert and then a check engine light. Checked the cap and it was on tightly.
Was thinking they might have over filled a bit, so drive around and burn off some gas (bummer ) clear the code (P0455 large leak detected) and they stay gone, for a while.
Drive on a bumpy road with the suspension set to Sport+ and ding ding, up pops the check engine light again(happened twice), clear it again, drive to Portland that week (~400 miles) no CEL.
4 days later, driving home from work... CEL - same code P0455, clear it.

Go get gas today, get the check cap again and of course the CEL.

any ideas other than the gas cap?

 

Yes, it could be the gas cap. On another Porsche, had CEL P1486 (tank leak) at year 10. Replaced the gas cap (relatively inexpensive) and it resolved my problem. There is a rubber gasket on the gas cap that may have dry rot which is not easily visible. Apply some silicone grease (for O-rings) to lubricate the new gasket on the gas cap.

 

I changed the seal on the gas cap which was about 10 bucks and it still happened from time to time. Hopefully it isn't your HPFP because I got that same code when it was going bad.

 

At least you guys don't get the CEL when the tank is less than 1/4 from empty. These Panameras are crazy! LOL

 

well got my new cap, fits tighter and I thought it did the trick, drive to work and no CEL, first time in a while, but on the way home - ding! dang CEL again.
time to start looking, I'm hoping it that it is just something loose from when I did the thermostat housing.

 

Hopefully not you high pressure fuel pump

 

any other symptoms? before you found out it was the high pressure pump?

 

Will try to find code in guided fault finding. Will be nice to look into car work again.

Regarding letting the gas go down below 1/4. CC, in particular AMEX, may not fill the tank, so I hardly let it go so low...

 

Okay. So this is > 2mm diameter leak detected. It could be many small leaks that sum up to equivalent > 2mm

Sorry up front if I don't understand what I'm looking at!

First possibility is fuel cap which you tried.
The rest isn't so clear.

It notes system components:
Mechanical vacuum pump
Leakage diagnostic pump
Variable intake manifold (not Turbo)
Boost pressure control cycle valve (Turbo only)
Diverter solenoid valve (Turbo only)
Exhaust flap (if fitted)
Acoustic simulator (V6 Turbo only)
(EDIT- must be another page because wasn't there yesterday) Tank leakage diagnostic pump (USA, Canada, and South Korea only)

So first question, did you replace (with new ones) the 8 intake manifold gaskets? I replaced with aftermarket from FCP Euro. I remember now that they kind of easily slipped off if I wasn't careful. With not many many miles I did not replace them this last time I confess...

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Evap leak, and fuel pressure codes.....also car would bog out as if it were not getting fuel from time to time. It is pretty easy to tel

 

jzchen, yes I replaced the seals with new ones from FCP Euro as well, list gives me something to start looking at, thanks.

Mazurda, thankfully no other codes and the car runs beautifully and pulls like a beast hopefully we can rule out the pump (for a bit anyway)

 

 

hey Dogwood, why dont you take some pointy thin screwdriver, that wont cut into seal, lube it first and then try to rotate it, so that when closed, the seal does not contact same locations again. This rotation can help if seal is the issue, and if it is hardened in a place of contact. Costs nothing and may help. If that fixes it (would take while of observation and no other changes), then you replace seal. You can get the whole cap for 30 bucks or so, easy to swap (I even bothered with diy for it).
Does your CEL come on after you fill the tank at gas station? My CTT was getting CEL and after I filled fully, it would hesitate to start initially. It turned out to be the evap canister to replace (PTT has it on the edge of the engine valley, so intake would have to come out).
Lemme know.

 

OK, it's getting more interesting, so as I stated earlier on Monday I tried it with my new gas cap, worked all the way to work, then on the way home I got a CEL again after driving a rough road.
SO I clear the cpdes, check and press on some connection I had moved when I did my thermostat housing, then check the gas cap, ok no cel the way to work again, then at the end of the bumpy road - CEL.
Hmm once, maybe, twice, showing a trend. (on the road I was in either sport or sport+ suspension settings)

Got home cleared the CEL, didn't do anything else, had to run a errand, twice as far as my commute, drove there, no CEL, came home, no CEL.

seems as something is just a tad loose or something.

 

Have a pic of the connection, or what it's for? My loose connector was about 2-3 mm from being seated. I figured it out only because as I was pulling it off to possibly replace the fuel pressure sender something felt strange, so I fully engaged it. Once I did that I tried to remove it again but it was stuck/I had difficulty removing it! It had easily come off the first time.

Hoping this is as simple as fully seating yours as well! Please keep us abreast...