Did a search on this problem but still looking for more info. 06 S R52 101000 mi. got the gas cap light then the Service Engine Soon. Pulled the code and it was P0455. Replaced gas cap with OEM. Orig didnt look that bad. Replaced the Tank vent valve too. Installed correctly. Reset code. Side note, I discovered that the ignition must be ON but the engine NOT running to reset code. I used Torque app with bluetooth dongle on the OBD port. Things good for only a few miles until the gas cap light came back on. No service engine light yet. So my question is: has anyone else had this problem and fixed it or had it fixed, using something other then the parts mentioned above? The service manual mentions something about a smoke test for leaks. Trying not to do that! TIA.

 

That's a major leak in the evap system! A leak that large probably wouldn't need smoke to find it.

If you know what components make up the evap system, just check all the components and find what's broken.

FWIW, when my car threw that code, the new OEM gas cap fixed it.

 

There's a purge valve at the front on left of engine. Also the leak detection pump can leak causing its own fault. It is located in back under car in front of back wheel. A smoke test may save you from firing the parts cannon.

 

here is a link to a smoke tester that i saved some time back...

not sure if it would work for your application. never smoke tested the evap system. may take some creativity...

https://www.ebay.com/itm/264134468462