HI guys,

I have a 2007 Carrera S with 17,000 miles. I am the second owner and don't drive it much due to heavy work load. I was getting low on fuel so I filled the tank to the half-full mark recently with Premium. Soon after that I got the P0456 small evap leak trouble code. The car ran fine at this point. The gas cap was original and the attachment strap was broken, so I replaced it with a dealer supplied cap. After clearing the codes with my OBD2 reader, the code came back immediately upon restart, but the engine was still running as usual –– smooth and strong. I read that the purge valve is what caused most of these CELs so I decided to replace the valve with the correct one from Bosch, using the original vent lines. I was a tricky job, but upon testing the old valve I found it was leaking, so I'm glad I replaced it.

After reassembly I started the car and it immediately shut off. I started it again and I gave it a bit of throttle and it ran extremely rough then died again as soon as I lifted the pedal. So, I retraced my steps. I cleaned the MAF, and checked its voltage, which read 12v on my meter. Then I removed the throttle body and used a flashlight to shine under the intake plenum while looking through the TB opening. First problem found! I had not re-attached the right-hand TB crossover tube into the rubber boots at the front side (towards the front of car) all the way. I reattached it correctly this time and put it all back together again. I restarted the engine and the same thing happened! Rough running and won't stay running without pedal pressure. The CEL is still there as well.

Is there anything else I can check? Should I fill it full with fuel? I suppose it is possible the old vent line has a crack, but the car only has 17,000 miles and the line was still flexible. I guess it is possible that the left side of the TB crossover tube is also installed wrong, but assuming it has no gaps, what else could it be? This is definitely a big air leak.

Also, some forum replies have suggested the charcoal canister leak detection pump is the problem, but I'm not getting a code for that. And this model does not have the vent line next to the fuel filler neck so it can't be that either. Thanks for any help you can give me.

 

If you have a smoke tester, you will find the problem in about 30 seconds.

 

Based on what you've described, there's a problem with the new purge valve or hoses to it or you have a major vacuum leak.

As suggested, a smoke tester will rule out the vacuum leak or show you where it is. The rubber sleeves on the intake manifold crossover and throttle body are challenging to get on and clamped correctly if you were in that area.

 

I made a cheap smoke jar and found the leak! As suggested, it was my error. I did not get the crossover tube secured properly. Now she starts up and runs smooth as usual. BUT, I still have the P0456 code. Is that supposed to turn off after several drive cycles? It's raining heavily here so I won't be driving the car until the weather clears.

I have popped the lid off of the charcoal canister box. Those clips fly off if you're not careful. Two of them hit the underside of the bonnet and bounced twenty feet away. Could it be the vapor pump, even though the code is for a leak? The pump and hoses look okay, but does anyone know how to test it? Those are pricey little guys, so I want to know for sure if that's throwing the 0456. Otherwise I'm out of ideas.

 

Update. I have now replaced the gas cap, purge valve behind the alternator (stupid place to put it), and now the leak detection pump. P0456 comes back after startup. I have a cheap OBDII scanner and have cleared the code many times by now, and it comes back immediately. Does anyone know if a better scanner, like a PIWIS, will clear the code, or pinpoint the leak? Maybe the line from the purge valve to the intake is leaky, but the smoke did not come out of that section. Thanks for any suggestions.

 

Success! I could not get the code to clear using my cheapo scan tool, but I decided to try the battery cable cross-wire. I'm not entirely sure this wouldn't have worked by simply disconnecting one or both cables, but after I ran a jumper between both battery cables (cables off the battery of course) for about one minute, the code was gone. I drove it around the block and still no code. I'm calling this done. Hopefully, no more pesky emission codes come back to haunt me. Thanks for all the advice, even to previous posters from years ago who helped a guy from the future.

 

Update: The 2007 Carrera just popped a new code, P0455, major vapor leak. To recap quickly, I replaced the gas cap, purge valve and leak detection pump in December due to the minor leak DTC. Now I am getting the major leak. I just tried rubbing a light film of oil on the fuel filler neck and tightened the new cap with 3 clicks. I cleared the code with my scanner and it came back upon startup. VA997.2 had a similar issue and found cracks in the fuel pump flange. His car is a 997.2, but mine is a 997.1. Does anyone know if the parts are the same or does the later model use a different part? Are the early 997s also prone to the cracking of the pump flange?

I don't know what else to check, and I don't have my crude smoke can anymore, which barely worked anyway. Thanks.

 

Not to discourage you, but I have had an intermittent P0456 leak for approximately 10 years. I have had two topnotch Porsche-trained mechanics (one in Seattle, one in Nashville) smoke test it to no avail, then suggest parts to change, mostly on hunches and definitely not as a result of the smoke tests. Starting with the cheapest parts (now three different gas caps) and moving towards the most expensive in the EVAP system, nothing affected this intermittent code at all. Rather than blindly swap out even more expensive parts on a hunch, I have come to prefer an accurate diagnosis which has not been forthcoming. I did put in a Bluetooth OBDII reader which is always installed on the OBDII port, and I can quickly clear the CEL whenever it pops up -- approximately once every week or so. Nothing has gotten worse and nothing has gotten better. The engine runs just fine. And that is where the situation stands at this point.

The only real problem I have had with my kludgey setup is whenever I was required to get a smog test (in Washington State) I had to wait after the CEL reset for a few days to make sure the system normalized and did not report a recent, suspicious reset. Of course, since I moved to Tennessee, Washington State has now done away with regular smog tests for licensing.

 

JustinCase, thanks for the Bluetooth suggestion. My HF code reader doesn’t clear emissions codes, so I may have to get the Bluetooth one. In the meantime I cleared the light by disconnecting both battery cables for a minute. Doing that always results in a warning about the PCM. That should go away after a few minutes of driving.

I sure hope this is not my new normal!

 

This is the one I have . . .

 

About six months ago I had the P0456 code, along with intermittent rough idle and engine dying.
Car ran fine if I got above idle, but it started getting worse.
Put up with it for about a week, then replaced the AOS (Air-Oil Separator) on the right side of the engine towards the back, under the intake manifold.
Wasn't much fun doing it, but no more P0456 and the engine runs perfectly.

I'm not saying my problem was the same as yours, but only offering it a possible insight to your problem since you seem to have logically replaced parts.
A good test is to try to remove the oil fill cap while the engine is running. If you can't remove it then it's likely a defective AOS. Do a search on it.

Best of luck sir!

 

Thanks for the suggestion. I just went out to check the oil cap at idle. It came right off, so hopefully no AOS issues. I had to replace it on my '02 Targa, and it was not fun. (Dropped the engine to its lowest point and attacked from the forward side of the engine.)

PCM went away today, but not until I had made two trips around the block and turned the car off between trips. On the second trip I increased speed over 35 mph, and that did the trick.

Thanks again to my Porsche friends!

 

agree I used a Obd2 to help direct efforts .