Another CEL P0446 question

[Rob175]

Well...after getting a P0446 code on my 98 Boxster a couple of months ago I replaced the old gas cap with a new one after noticing the o-ring inside the cap has some cracks.

After the old cap was replaced and the CEL code cleared, I drove the car for the next couple of months assuming the problem was solved since the CEL never returned....UNTIL TODAY. As I was driving to its "winter storage" location the CEL P0446 returned.

Question: Can topping off the fuel (beyond the gas station's fuel pumps "auto-shut off") cause fuel to mess with the evaporative canister and trigger a CEL P0446 ??

(note: About a week ago I topped off the fuel tank in preparation for its winter storage and drove it for about 30 miles afterwards)
(note: The new cap is an OEM cap)

[JFP in PA]

Originally Posted by Rob175

Well...after getting a P0446 code on my 98 Boxster a couple of months ago I replaced the old gas cap with a new one after noticing the o-ring inside the cap has some cracks.

After the old cap was replaced and the CEL code cleared, I drove the car for the next couple of months assuming the problem was solved since the CEL never returned....UNTIL TODAY. As I was driving to its "winter storage" location the CEL P0446 returned.

Question: Can topping off the fuel (beyond the gas station's fuel pumps "auto-shut off") cause fuel to mess with the evaporative canister and trigger a CEL P0446 ??

(note: About a week ago I topped off the fuel tank in preparation for its winter storage and drove it for about 30 miles afterwards)
(note: The new cap is an OEM cap)

P0446 has nothing to do with the gas cap, it is for the EVAP canister shut off valve function being below the lower flow limit. It indicates that the purge airline is blocked or the EVAP canister flow is blocked.

[Rob175]

Thanks for the reply BUT every description of issues causing the throwing a CEL P0446 code says check or replace the fuel cap or its o-ring FIRST. Additionally many (not all) reported that after they replaced the gas cap they no longer had the P0446 CEL code.

I realize a new cap didn't help everyone but certainly it did for many reporting as much.

I was just asking if filling the fuel tank ...or even "overfilling" the fuel system can cause a problem with the evaporative canister.......somewhere in my mind I seem to recall reading of that possibility after filling up too much.

[JFP in PA]

Originally Posted by Rob175

Thanks for the reply BUT every description of issues causing the throwing a CEL P0446 code says check or replace the fuel cap or its o-ring FIRST. Additionally many (not all) reported that after they replaced the gas cap they no longer had the P0446 CEL code.

I realize a new cap didn't help everyone but certainly it did for many reporting as much.

I was just asking if filling the fuel tank ...or even "overfilling" the fuel system can cause a problem with the evaporative canister.......somewhere in my mind I seem to recall reading of that possibility after filling up too much.

Everyone perhaps, with the exception of the factory OBD II diagnostic's manual, which says what I told you.

[spinjockey]

If you’ve overfilled your tank and it has saturated the evap canister or the lines then you can get this code.

[Rob175]

Spinjockey....If that's the case...will the gas remain there or eventually evaporate or flow into the tank to be used by the engine and return to a normal condition (ie: no more CEL triggering)?

Or…… would it be wise for me to loosen or remove the gas cap for a couple of days to hopefully let some of the trapped fuel in the canister evaporate??
Thx

[spinjockey]

Originally Posted by Rob175

Spinjockey....If that's the case...will the gas remain there or eventually evaporate or flow into the tank to be used by the engine and return to a normal condition (ie: no more CEL triggering)?

Or…… would it be wise for me to loosen or remove the gas cap for a couple of days to hopefully let some of the trapped fuel in the canister evaporate??
Thx

You need to purge the lines. The gas won’t evaporate on its own and it’s effecting the rest of the evaporation system performance. You might have to replace your charcoal canister if it’s saturated. In general you should never overfill these cars because the evaporation systems are complex and unforgiving.

[Rob175]

Well.....the car is in "winter storage" now and my access to it is very limited, so I'll just have to deal with it in the spring, about 4 months away. I know the waiting will drive me nuts!

[spinjockey]

Originally Posted by Rob175

Well.....the car is in "winter storage" now and my access to it is very limited, so I'll just have to deal with it in the spring, about 4 months away. I know the waiting will drive me nuts!

You awaken in the spring to the boxster howl.

[Rob175]

I just discovered that because my 98' Boxster has what Illinois calls "Expanded Antique" license plates I am exempt from the "every two years" emissions tests, which I would have surely failed......so once spring comes and I can start driving again I plan on driving it for a few weeks to see if the CEL (which I cleared using my code reader) reappears.

I had this same code about 3 years ago and just kept clearing it....then at some point it just stopped lighting up the CEL with that code and for the last few yrs its been fine.....UNTIL I mistakenly really topped off the tank for storage.

That's why I asked IF the trapped fuel in the canister will evaporate on its own, thinking thats what happened a few yrs ago.

Thx

[spinjockey]

To answer your question it does evaporate but what happens is that the charcoal gets saturated and eventually turns into a clay like substance. It stops being able to hold vapors from the gas tank and the purge valve underneath the manifold has a harder time evacuating the vapors resulting a purge valve failure or constantly open. A purge valve failure can lead to a hard start after fueling when hot and the infamous boxster howl.

[Rob175]

So.....its sounds like I'll be taking it to my indi shop in the Spring, when it comes out of winter storage. Probably will need to replace at least the canister and possibly a new purge valve too.

What's strange is that I've had the CEL and this code a couple of times over the years and haven't done any repairs and eventually the CEL "magically" didn't come on again.....until the other day after overfilling the fuel tank recently.

I'm not a DIY so off to an indi it will go in the Spring.

The only "good news" is that since I have what the state calls an "Illinois Expanded Antique" license plate (for 25+ year old cars) I am NOT REQUIRED to get a bi-annual emissions test, where any sort of CEL will cause a failure of the test until fixed.

[theiceman]

always stop at the first "click"

As it becomes more contaminated you will find you cant fill the tank and the pump keeps shutting off as you try to fill it as the contaminated charcoal is plugging up the vent.

Couple of lessons here outside of all that .. it is always courteous to state the definition of the code you are fighting , don't make others go look it up since you are the one asking for help .

Secondly it is best to just stick to what you are seeing and let people comment, rather than have them confirm your theories. ( just the facts ma'am, just the facts)

As i have been a technical troubleshooter for over 40 years and tech technical troubleshooting , i thought these tips might help

cheerio.

[N227RV]

We may all have to replace the canister one day. Is there a DIY guide available?

[Rob175]

"Theiceman"....thanks so much for "schooling" me on how to write a question post....your advice is "invaluable"......

[spinjockey]

Originally Posted by N227RV

We may all have to replace the canister one day. Is there a DIY guide available?

I haven’t seen a DIY. I replaced mine chasing down the infamous Boxster howl. It’s not hard as the canister is easily accessible from the front passenger wheel well. The real problem is that there a few variants in evap canister over the years so you need to know which part that you need. This can be decoded from your VIN. When I replaced mine it was an hour tops with most of the time spent disassembling and reassembling. I did weigh my old and new canister. The old canister weighed a whole pound more than the new canister.

[tcoradeschi]

Originally Posted by N227RV

We may all have to replace the canister one day. Is there a DIY guide available?

Bentley manual, section 24.

[Starter986]

Originally Posted by Rob175

"Theiceman"....thanks so much for "schooling" me on how to write a question post....your advice is "invaluable"......

I believe he's well meaning. He and I may have gotten offf on the wrong foot... but he may be working on loosening up.

Slightly I vetted him... and he's a smart personality. I'll be paying more atttention to his advice and recommendations. He knows his stuff.

[Rob175]

Well, unfortunately for me, the correct "charcoal vapor canister" part (based on my VIN number) goes for about $1,000.

(note: The car is stored away for the winter so my conversation with my "indi" was just a conversation without actually scanning the car.)

Additionally, my "indi" suggests a couple of valves in the system should probably also be replaced at the same time because "they too are 25 yrs old, possibly problematic and as long as we're in there......".

I'm wondering if professional scanning equipment (much better than my little hand scanner) will also determine if those valves are working properly? Or, as the "indi" suggested, it was best to just replace the canister and the associated valves adjacent to the canister at the same time. (the valves are not very expensive (relatively speaking).

[JFP in PA]

Originally Posted by Rob175

Well, unfortunately for me, the correct "charcoal vapor canister" part (based on my VIN number) goes for about $1,000.

(note: The car is stored away for the winter so my conversation with my "indi" was just a conversation without actually scanning the car.)

Additionally, my "indi" suggests a couple of valves in the system should probably also be replaced at the same time because "they too are 25 yrs old, possibly problematic and as long as we're in there......".

I'm wondering if professional scanning equipment (much better than my little hand scanner) will also determine if those valves are working properly? Or, as the "indi" suggested, it was best to just replace the canister and the associated valves adjacent to the canister at the same time. (the valves are not very expensive (relatively speaking).

The valves and lines can be tested individually, but not by a scan tool, it requires getting your hands dirtty removing them, blowing air through them, and testing them electrically; you know: Diagnositcs, which mechanics do while parts swapers just replace things randomly, hoping for success...............