Diagnosing P0440

996 C4 with about 98,000 miles. My Durametric read a 0440 code with a check engine light yesterday. This is "Porsche Fault Code 93 - Fuel tank ventilation minor leak". No other symptoms to report; starts right up, no problem fueling, runs great. I cleared the light and drove about 50 miles today, then filled the tank. When I got home, there was still no CEL, but the Durametric *did* read the 0440 code again. It's cleared again, and I can keep an eye on it... But how can I diagnose this code? I've read some things which imply it's the regeneration valve, some things say it's the shutoff valve, some say it's the bleeder valve.

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it could also be a bad gas cap.

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Could be the cap seal, but the cap's on tight and is only two years old.

This string below includes the Porsche troubleshooting flow chart for code 0440/93. However before spending a lot of effort or worry on this, I'd monitor a bit and make sure I always tighten my gas cap (lots of clicks.) Also, look at the sealing ring on your gas cap. Any cracks or just look old and tired? Replace. I have a 2000 that I've owned since 2001. Every couple of years, I would get a 93 or 94.) For me, the codes were never persistent. Clear the code, tighten the cap, no more codes. Though about four years back I bought one of those shinny new caps, just cause it looks good. Don't think I've seen a 93/94 since. https://www.renntech.org/topic/43496...nd-code-p0440/

As I mentioned, the cap is about 2 years old; the O-ring is in good condition, and it's always tight. I saw that thread -- it got me lost. Have you done any of those things? How do you "check EVAP canister purge valve", exactly? Or "check triggering of EVAP canister purge valve"? When you followed those steps, what did you specifically do in order to test? Plus, though the instructions say to work the purge valve, the OP in that thread says they replaced the regeneration valve, instead. The instructions I have are here and have some more detail, but require two or three special tools ... and still don't mention the regenration valve in the thread you've linked.

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The fuel tank and fuel tank ventilation system attached to it, is a sealed system to prevent fuel vapors from escaping into the atmosphere (emission standards). Because it's a sealed system, it needs a way to vent as the fuel level either drops so the fuel tank doesn't collapse or expand as the level in the fuel tank changes from either using up fuel, filling up or expansion if the fuel gets warmer. The way they do this is by allowed air to come and go from the tank through various hoses and valves to allow for changes in pressure. What you're basically doing is trying to find out if there is a leak somewhere. Found this online and it may help. Sorry I can't help more, it's tough to explain it all online without some sort of a tutorial. https://www.6speedonline.com/forums/...lp-needed.html

The purge and regeneration valve are likely the same thing. It's activated with an electrical voltage to 'pulse' and allow it to 'purge' but is normally closed, I believe. So it should hold a vacuum when not in use. This video is not for a Porsche but almost all purge valves work the same way. Hope these help. You Tube

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As far as I can tell, they're two different parts. The regeneration valve is 996-110-129-53 and the purge valve is 996-605-201-01. What leads you to believe they're the same part?

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- yeah, I know. The image below shows the whole system. No regeneration valve. And there are two purge valves though item 7 is called a Bleeder valve in the parts diagrams and item 1. is the EVAP canister purge value Note: I've added some comments in-line above. Here is what I'd do: 1. Study the Porsche manual, drawings, and parts lists to familiarize yourself with the system and components 2. Inspect components likely to be causing the problem, remove, clean, inspect, check valve movement and reassemble or replace if anything seems suspect. . I'd start with the components under the fender, especially that bleeder valve and then that Evap purge valve. Please keep us posted on what you do and find. Thx

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Sometimes different manufacturers call them different things and having been out of the game for a while I wasn't sure. It doesn't really matter what they're called, though. The diagram KeyWest shared (which I tried to find last night - good job!) shows what you're dealing with. You need to find a leak in an enclosed system. It might be difficult though, if you don't understand the system and where all the connections are and how they work.

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The 'purge valve' at the tank may be sometimes called a regeneration valve. Does that valve open to 'purge' or regenerate the canister? Where did you find that pic and is there a larger one available?

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It was on a Rennlist string but I found it doing a google search. I'm sure I can find it tonight in the manual.

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I used to have all the factor manuals up until the early 90s. The were all destroyed in a flood.

Gentlemen, check out this thread. I think the OP's problem was more serious than what we are looking at here but this provides superb overview of how the system works, what the various parts are, how he bench tested valves and such. Really informative. Tons of photos, drawings, etc. https://rennlist.com/forums/996-foru...em-pics-8.html

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How did you arrive at that? The pictures there look like the ORVR system (M664); I have the OBD2 system (M660).

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- did you scroll down to the parts about the evap system? What he describes is the exact system I have in my 2000 C2 and is very helpful in helping me understand the Evap system in my car, how it works and how he troubleshot it. If there is nothing there that helps you, my bad.

I ended up replacing the regeneration valve (996-110-129-53) and the small vent line leading to it (996-110-127-31). The old valve would pass air at all times, even when energized. Energizing the valve wouldn't cause an audible click, either, and would draw about half an amp of current. It's been a couple weeks, and the car hasn't logged a fault since.

I now own this car and I have seen P0440 come up 3 times since 8/2023. It's funny this thread is the first thing that shows up when I started googling the problem Reading this thread: https://www.renntech.org/topic/47193...e-replacement/ , I have also noticed an intermittent whistling at light/medium throttle, but since the p.o. had already replaced the regeneration valve, I'm not sure if I should look into replacing that again (because the whistling), or check something else like the purge valve. ( 996-605-201-01). I wonder if that could make a similar sound if there's a leak? Btw, looking at the 0440 pdf linked above, are there two separate part numbers for the 'shutoff valve' and the 'purge valve'? The pdf seems to imply that, with step 1 saying check shutoff valve, and step 3 saying check the purge valve, but googling seems to show they are the same thing. I see the same part numbers being sold as 'vapor canister purge valve' and 'vapor canister shutoff valve'. Confusing

Edit: See post #21 and ignore mine below... It's 2 descriptions for the same part, each describing one of the two possible states the valve can be in. Open to purge the cannister and closed to shut it off. Different p/n could be a revision or the difference between the p/n on the valve itself and the p/n as used to order as a spare part.

A challenge with troubleshooting this particular problem is the nomenclature. And it is a rather extensive system. Without the part in hand with a part number on it, it feels like we are just guessing. With that said, almost all of the Porsche troubleshooting guides start with some form of a) inspect b) check for proper installation and c) check operation. All before purchasing parts. I'd recommend that approach. The advantage of this is when you have a part in hand, you have a part number. Even if it's been superseded, there is no guessing as to what it is and finding the troubleshooting procedure is much easier. I'd also start with the area/part you know has been replaced or messed with. With your case, it is possible that Mike never got to the underlying issue but I'd still start with the work that he did and go from there. In my case, when I had same problem code (which led to my interest with the original string), my first thought was, oh boy where do I start? And what parts should I have on hand? But I had had Porsche paint my car a couple of years previously which involved a lot of disassembly. I knew they had taken out the wheel well trim so I started there. Sure enough, they had broken (and sloppily) repaired the valve right behind the fuel filler neck. My inspection quickly found the problem. I was able to super-glue the part as a temp fix. While I doubt you have the same problem, my point is, I know I like to have parts handy for a repair, especially when it can take me two weeks to get a part but sometimes you just have to get in there and systematically inspect and test.

This is the shut-off valve ( located near the carbon canister) This is the purge valve/regeneration valve located near the throttle body ;; Code P0440 is a code meaning a small leak "anywhere" in the tank , lines, filler neck, cap,carbon canistor , or vent system as judged by the pressure sensor mounted to the top of the tank... That said, the most common thing I have found is cracks in the fuel pump/gauge cover/lid/housing...Fill the fuel tank all the way full, then drive around just a bit, then remove the battery and battery tray and see if it is wet on the top of the fuel gauge cover....If so there is where your code is coming from. Put it back together and drive the tank down to half tank then replace the fuel gauge/cover...

I've edited my post based on PT3's clarification. Your pictures are much appreciated!

Thanks everyone, I really appreciate all of the suggestions! I need to replace the front-right fender liner anyways, so I'll take a look at everything there and under the battery while I'm replacing it. Hopefully its something obvious

Try smoke testing your fuel tank. I tried all the usual suspects and it turned out that the fuel level housing that is located under the battery tray had a small crack in it that was causing an intermittent leak. My mechanic could see the smoke slowly appear from that area. I replaced the unit and have been CEL free for few months now. Took me like 3 years to find this bastard of a leak hah

Welp, car wouldnt turn over today, after I went to pick up my friend and turned the car off momentarily. I had been driving it all morning without issues. It had a little under a quarter tank, and I remembered reading about people having issues starting on near empty(or full?) tanks in these evap code threads. Luckily I was near a gas station and brought 2 gallons over, and after adding it the car started right away. !! I went to the gas station and filled it up to full and started the car 5-6 times no issues. I might not get the issue diagnosed or fixed before the track days i have coming up, so I guess ill just have to bring a few tanks of gas with me

Fender liner just got here so I'll take a look soon. Also, P0446 showed up today... not sure if that narrows down the problem at all.

I had some trouble starting yesterday at 3/4 of a tank, so its not just a low fuel problem. It eventually started when I pressed the gas to the floor while turning the key for 5-10 seconds. Also, I took a look at the top of the fuel tank just now This was all there was under the battery tray.. Not much interesting there, looks pretty dusty and dry. The tray in front of the battery covers what I assume to be the top of the fuel gauge assembly, this looked a lot more interesting and is what I think you guys are telling me to check under the battery tray for It also appeared pretty dry. I assume any liquid accumulating here would be leaving some signs in the dust. Of note, there was a bit of hot glue around the black ring. I thought, could this be covering up a previous crack? Removing the glue and cleaning up the area a bit, it seems pretty unremarkable. Doesn't look like theres a crack there, atleast nothing visible to my eye. I might try liberally applying hot glue to the area just in case. Also looking at part # 1J0-919-133-A-M253 , the 'sealing ring for fuel tank level sensor', that might be sitting under this black plastic ring? It could be pretty old I guess Anyways I feel like a complete noob, I've never dealt with evap/fuel issues before. I would appreciate if someone could validate I'm looking at the right thing, and if I should rule this out for now and focus on checking the other areas.

Ok I don't want to just shoot blindly in the dark here. I'm getting a smoke test done tomorrow morning, hopefully that will find the problem

^^^ is the correct way foward.

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You must have a C4 or C4S because you have an AWD fuel tank. The hot melt glue on the nut is the factory tamper evident seal. The sealing ring, I have never heard of one going bad. I just took one out of a 32 year old VW (same part) and it was good as new. You should remove the fuel pump and inspect the in-tank lines. Tbere are lots of them and they can crack, causing all kinds of problems including hard start or no start.

Smoke test was done this morning, heres what the shop said: Operating off of notes that P0440 and P0446 were stored codes, removed regeneration valve (evap canister purge valve) to access vapor line to install smoke machine to check integrity of rest of system. When purge valve removed, checked flow of purge valve in off state using breath. Found with solenoid in off state, some flow was still possible through valve. Electrically actuated solenoid while breathing through and found solenoid still functional, and flow changes, however flow being possible in off state is a fault in the part. Installed smoke machine to vapor line, applied smoke through EVAP system, found no immediate signs of leakage anywhere else. P0440 indicates an excess of vapor flow when not commanded. P0446 indicates lack of airflow through vapor canister. After Purge valve repaired, recommend evap system self test as P0446 may have been set as a result of P0440’s symptoms. The 'regeneration' vs 'purge' valve nomenclature is still really confusing!! They clarified that part # 996-110-129-53 is the faulty valve, which is the part the PO has already replaced once before. I guess these things are pretty unreliable... I'm going to order a new bosch unit and reusing the long tube from the oem porsche part, replace it myself. .

Got the old valve off and i can confirm what the shop said, i can blow air through the old one but not through the new one. Managed to reuse the old hose too, since the part without the hose is $200 cheaper