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Old 01-19-2019, 03:18 PM   #1
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What now?

1999 boxster 130k miles Po455 (gross leak) CEL

This is what I've done so far:
Replaced purge valve (engine under manifold)
Replaced Vacuum control valve (on side of EVAP tank)
Replaced carbon canister valve (on canister)
Replaced Fuel Cap (OEM)
Replaced vacuum valve (on filler neck)
Smoke checked the entire system. Took off underneath panels to check for leaks (none)

I'm at a loss. No signs of leaks anywhere. followed all lines as best I could. I have read everything I can find about this but I have done everything recommended.

I know there is a pressure differential sensor under the battery at the fuel tank. Could this be not working properly?

Any help would be appreciated. I'm ready to pull what little hair I have left out!

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Old 01-19-2019, 09:42 PM   #2
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Originally Posted by bob4a3 View Post

I know there is a pressure differential sensor under the battery at the fuel tank. Could this be not working properly?
In my reading, it seems this could indeed be the culprit.
However: are we sure the fault code is real? By that I mean, are we sure you have a leak? Or is it possible you have a sensor issue? Do you hear hissing when you remove the gas cap at the fill station? Do you smell gasoline when the car is running?

I assume you've cleared the code since replacing all of those items, and it's returning immediately?

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Old 01-20-2019, 07:04 AM   #3
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Thanks Maytag,

Don't know for sure the code is real. No hissing and no gas smell. No trouble filling with gas.

I used a smoke machine and can't find any leaks. I reset the code and it comes back as soon as the system tries to pressurize. CEL then comes on after code is set three times I think.

I checked that purge valve and canister valve work properly.
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Old 01-20-2019, 08:29 AM   #4
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Thanks Maytag,



Don't know for sure the code is real. No hissing and no gas smell. No trouble filling with gas.



I used a smoke machine and can't find any leaks. I reset the code and it comes back as soon as the system tries to pressurize. CEL then comes on after code is set three times I think.



I checked that purge valve and canister valve work properly.
If there's no hissing when you release the gas cap, that suggests the fault is real. If your system isn't vapor-tight, then there's a leak somewhere. As to how to find that..... you've already done what I would do: smoke it.
Did you smoke it from a single source? ie: one side of a check valve but not the other? I'm just thinking out loud here. If we know the tank isn't pressurizing, maybe build a cap with a fitting that you can hook the smoke machine to. I'm just thinking trying it from a couple of different places.

Otherwise, I'm no help. I'll be watching with interest and hope someone smarter than I chimes in.

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Old 01-20-2019, 10:20 AM   #5
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Thanks I'll keep at it. Can't stand to be defeated.
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Old 01-25-2019, 06:51 AM   #6
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Smoked again from different locations. Still can't find a leak. Replaced pressure differential sensor today. Let's see what happens.
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Old 02-01-2019, 05:12 AM   #7
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Still get CEL P0455. Can anyone help?
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Old 02-01-2019, 06:46 AM   #8
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Did you look under the battery tray for leaks?
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Old 02-01-2019, 10:35 AM   #9
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Yes checked that and the lines under the shields on the bottom of the car.
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Old 06-06-2019, 06:18 AM   #10
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Did you ever figure out the problem and fix the P0455 code? I'm sure curious if you got it fixed.
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Old 06-06-2019, 08:38 AM   #11
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This may be obvious, but did you replace the gas cap?


Edit: OOPS, I just read that you did. Sorry!

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