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Evap Fun with P0455 Porsche Error 94

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My Evap system is once again on the fritz, I posted last year trying to solve a CEL P0442, And after cleaning my Regeneration valve (valve near the throttle body) and having that code go away, I am now trying to track down a gross system leak triggering a P0455. I bought and installed a new regeneration valve, as I figured maybe the old one just failed; not the case. Here's what I have conducted thus far, I'm hoping some of our evap system experts can chime in.


The light comes back on around driving 60 miles after resetting the light.

The Idle seems a little irridiac at stop lights, I'm talking maybe an 80rpm fluctuation up and down; something I don't remember the car always doing.

The Car won't fill up a fill tank with one continuous fill up, It generally clicks off 3/4 or 7/8 full and I have to slowly fill the rest of the way or turn the handle upside down.

The regeneration valve, the one next to the throttle body in the engine bay, If i disconnect it, and run some compressed air through it towards the evap can, I can hear the air leaking out around The front passenger under hood area, is this normal? Should the system be sealed with the car off? Is this the evap can? Where does the line that connects to the regeneration valve in the engine bay start?



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See attached diagram of the fuel system.  http://www.autoatlanta.com/porsche-parts/hardparts.php?dir=996-99-05&section=201-01 Difficulty in fueling may be linked to the vapor recovery valve or bleeder valve, Part 12 and 23.  They are located behind the right front fender liner.  Your description of using the compressed air and hearing a sound in front leads me to think that one or the other of these valves is faulty.  It also sounds like you may have a vacuum leak somewhere and those are difficult to find.  It could be related to one of those two valves.

Edited by DBJoe996
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I had the same problem and It turned out to be the fuel line vent valve. One symptom the car may experience is a sound as though one is blowing across the top of a bottle. Another symptom I noticed was a kind of a honking sound when I would turn off the car almost like the sound a balloon makes when you let air out of it while pinching the escape opening. I don't know if you're experiencing this but in my case, it turned out to be this part and when I took the old one out, it had dirt big time around it and some webbing from a spider (the dead and desiccated spider was actually visible!!!!). Have you noticed any change in your exhaust note ?

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Pressed, you had the same error code? I'll pull the wheel liner and take a look at the valve, the car is a garage queen; so I's totally possible a spider has found a home in my vent valve.


When would you hear the bottle blowing sound? Car on warm? Shutting car off? A few people talk about a gas cap suction test, but i couldnt find anything on how exactly that test works.


Porschedane, do you have a link to the one you bought or used? all the ones I've seen the nozzle is too big to put a piece of house over.


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Yeah bro, I had that very same P0455 goin on. I'm just sayin that it sounds like your situation may be the same but emissions issues can be very complicated sometimes, like chasing gremlins. I would hear the bottle blowing sound when I would park and turn the car off after driving about 15 minutes to work (short commute). One thing I also noticed is that the exhaust note had changed. I have GHL high performance mufflers on my 1999 996 and this "whirring" sound was very audible when the failing fuel line vent valve was still in the car and cancelling out the GHL exhaust note (at least that's how my ears perceived it). Difficulty filling the gas tank ? That's another symptom (see pelican parts DIY replace fuel line vent valve). I printed out the Pelican DIY article and studied it over and over until my confidence was up to snuff (this was my very first DIY). The fuel line vent valve normally retails for @ $85.00 or so. I purchased mine from Specialized German out of Rancho Cordova which sells used parts for our rides for a reasonable price. I'm totally convinced that the gas cap and fuel line vent valve are major players in the P0455 code, notwithstanding the purge vent valve that you had purchased.

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  • 1 month later...

Hey all, I want to thank everyone's input and advice to tackling this problem, I have an update! I hope Loren or others can step in and give me some .02 and anyone else with this issue can hopefully learn from this.


I replaced the vent valve, while inside the wheel well i also inspected all lines and connections, everything was nice and tight, and nothing looked cracked or broken.


I buttoned everything up and reset the code, 60 miles later it came back. Discouraged and bummed I starting tracing the purge valve line from the engine towards the front, and i blew some compressed air into the line. I could hear air leaking at the battery compartment. Pulled the battery out and looked at the fuel pump hoping to find something unplugged; of course that would be way to easy. I found this insted.


The nipple on the fuel pump, that connects to the evap line, that connects to the purge valve, was completely broken off, and the line was just resting against the pump.



My question to all, The part number is a "996 620 022 00" however pelican shows nada. Is this part of the pump or the sender unit? Can I this piece without replacing the entire pump? WHY IN THE HECK IS THIS PLASTIC?!


Thanks to all who helped track this down, now i can't wait to get everyones option on how to fix it :)




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  • Moderators

Unfortunately, you will have to replace the entire pump, and I would suggest getting it from board sponsor Sunset Porsche ( 1-888-502-5927) rather than Pelican.


Nearly all modern cars use plastic extensively on their fuel systems, simply because it is lighter than metal.

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