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Error Code P0455, and trouble starting after filling up

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My car (2008 Carrera S, Manual, 85k miles) threw a check engine light a few days ago, with the P0455 error code. I’ve read a few threads on this forum about it and the feedback Loren gave, but I wanted to share one weird symptom and see if that may point at something specific.


Every time I fill my car with gas (and this started a few weeks ago, I fill up weekly), the car won’t start. It cranks with gusto, but no joy. I have to give it gas to get it to turn over (and then it roars to life). This only occurs after filling up (and no issues with the actual fill up). Once it starts, everything is really back to normal until I fill up again. 


So, I was wondering if anyone else has seen that particular symptom and if that may point to some specific cause of P0455. I did replace my gas cap this week after the error first appeared (it needed to be replaced anyway), but that didn’t solve anything.


On the bright side, when it threw the error code I took a look in the engine bay I noticed my belt had a bad split down the middle. So, I replaced it this morning and avoided a much a worse problem!

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P0455 Leakage in fuel tank system


Possible fault causes:
- Tank cap not closed correctly, leaking or missing
- Purge air line leaking
- Tank vent leaking
- DMTL (Tank Leakage Diagnostics Module) leaking

- Leakage in fuel tank system


You might need a smoke machine to find the source of the leak.


The tank leakage test is performed only on USA vehicles.
Construction of the tank leakage diagnostics module:
The diagnostics module consists of an electric motor with a small air pump, switch-over valves, and a reference nozzle.
In addition, the module is heated so as to prevent the forming of condensation and ice.

The procedure of the function:
- The pump is operated via an electric motor and conveys air through the reference leak. The power consumed during this process is determined.
- The switch-over valve switches and the air current is now directed into the fuel tank. The power consumed during this process is also determined. After a waiting period dependent on the fuel tank fuel level, it must be at least as high as the power consumption was during the reference leak test if the tank system is leak-free.
- The system is identified by leaking if the power consumption is lower during the actual leakage test as it was during the reference leak test.
- An evaluation of the power consumption levels when the pump is started and after the switch-over valve has switched serves to identify faults within the tank leakage diagnostic module (e.g. pump blocked, motor spins at idle speed, the valve does not switch etc.).
- The diagnosis of heating, motor, and switch-over valve is performed via the output stage of the DME control module.

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Is the system the same as on a 996?  If so, the most common cause seems to be the vent valve contraption just below the filler neck.  I had the same symptom and replacing this vent valve fixed my 2004 996.  Mine didn't throw a CEL though, just wouldn't start after fill up.

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If they are not exactly the same I believe they are very similar. I'm going to dive in to that section of the car this weekend and see what I see. From everything I've read so far those components seem to be the most likely cause of the CEL. The only thing I hadn't found so far was first-hand experience with that start-up issue after filling up, so thank you very much for the feedback. I'll follow up with what I find.

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  • 2 weeks later...

To close the loop on this, the original problem was that after filling up my 2008 Carrera S (997.1), the car would have a really rough start (I’d have to give it some gas) and it would eventually roar to life. After about a month of having this problem inconsistently, I got a check engine light, which turned out to be P0455. I replaced the gas cap (it was old anyway) and no joy.


I did some nosing around myself, but didn’t spot anything obvious. I was short on time and patience, so I took it to a trusted shop. They did a smoke test and found nothing, so they did a manual test of a couple of parts.


The problem part turned out to be the Change Over valve (996.605.123.01), which is now part # H72031281. Cheap part, not too terribly hard to replace (not that I did it but that’s what my mechanic told me)... but a pain to diagnose.


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