I had a check engine light come on the other day so I plugged my obd2 reader in and pulled the code and it came up with the p0455 code which is a "P0455 - Evaporative Emission Control System Leak (Large Leak)". I tightened the gas cap and reset the code, it came back on. Went and tightened all the intake hoses and made sure they were all fit correctly, reset it and it came back on.

Has anyone had this happen and how likely is it the EVAP canister or EVAP control valve? I don't think it is a broken gas cap but not really sure how to tell if it is. I have done some research but mainly pull up v35 info. Any help would be greatly appreciated and how much should I worry about this code?

 

A gas cap would show up as a small leak.

 

The main reason I asked about the cap is looking up the code shows this:

 

Just to confirm a "gross" leak can be a missing or defective gas cap.
Evap codes can be difficult to fix, as we don't have smoke machines to help us find the leak.

I need to head out for a few hours, but will type up a few things you can try when I get back, assuming you want to try to troubleshoot this. This code is not one of those "P0xxx = replace xxx"

EC-313 http://www.nicoclub.com/FSM/G35/Sedan/2008/EC.pdf

 

I wanted to give an update also advise a program that anyone with an OB2 connector should get. Using my Dashcommand app on my phone hooked upto my wifi obd2 box ive cleared the codes a few times like ive mentioned to no avail.

However my dad has been a mechanic/Service Manager and above for over 40 yrs now and I asked him what the best way to rule out a the fuel cap without replacing it and since my car is 10 yrs old these days ( we all know most cars were built the the year before there model designation, aka a 2007 probably rolled off the line sometime in 06) had the idea to grease the Gas Cap seal as a dry seal on a gas cap will act the same as a broken cap since its dry and will misalign and do the same thing as a broken cap and not completely seal when tightened.

I used petroleum jelly around the gas cap seal and cleared the code. After pushing the car to throw the light and driving for a few days (knock on wood) has yet to throw a light since. Now I have an appointment at the dealer when I take in in for an oil change saturday (I don't have a garage to do the oil changes and for $40 I can handle swinging by the dealer). If the code throws again there going to smoke the system and do a check and advise to decide if its the canister or evap valve. If all goes well then I am good to go.

If not I will keep updating this for anyone that runs into this problem in the future.