Starting about a month ago my CEL came on after getting gas. I redid the gas cap in case it was loose. Eventually it cleared, but ever since then it comes on every tank, sometimes at random and goes away after a trip or two. I got the codes read and they were P0442 and P0455. These are the same coes I get everytime the dealership tells me I need a new gas cap and once replaced the car is fine for another 6-9 months before the problem starts up again and I get the same codes and they replace my gas cap. I'm now on my 5th gas cap!!! Well, this time my symptoms have progressed a bit differently than before, but I'm still pulling the same codes at this point. For the last three or four tanks my CEL comes on at roughly the 1/2 tank mark and stays on until it reaches the 1/4 mark and I get gas again, then goes after after usually one trip or even immediately after getting gas. Also, my gas mileage has taken a major nosedive. I was getting an average of mid 19s mpg going to and from work. Now I'm getting 16-17 since the CEL issue has popped up (started at the end of December). I'll need to get gas tonight when I get off work, but right now it looks like I'll be lucky to have gotten 15 mpg this time as I only have 191 on the trip when it hit the 1/4 mark. I've gone from having just under 1/2 a tank yesterday to just under 1/4 of a tank today in only 35 miles (it dropped three lines from the time I shut it off last night until I started it this morning with no visible leaks under the car), which is extremely ridiculous. I can't find anything obviously leaking or any strong fuel smells, but my gas mileage sucks and the CEL keeps coming on giving me the typical evap codes associated with the gas cap. Can a faulty gas cap cause the issues I'm having, or is it more likely I have a leak somewhere else in the fuel system?

 

you might be having some other evap leak. have the system tested

 

Symptoms do suggest there is a leak somewhere - could just be air escaping not gas .

Are there any dents on the steel lip where the cap screws on ?

 

Nothing that's obvious to me that it's damaged. I keep checking everywhere looking for damage or a site of leaking, but I'm obviously missing something or it's very small. I am probably going to end up taking it in to be checked in the next week or two because whatever the issue is, it seems to be getting worse.

 

Have a look under the bonnet - there are two hoses that go from the chassis to the engine on the RHS by the dipstick . One with a blue connector and one with a red . See if the blue one is pushed on properly . Just a wild guess - but worth a check .

 

Ever find out anything? mine seems to be doing the same thing as far as the engine light.

 

The problem could be the filler neck, rather than the cap. At some point they revised the threads on the neck to address that.

See the "MIL Illuminated - P0455 Set" TSB.

Ken

 

got cel yesterday.
have no code yet but realized how loose the cap was.
and this was replaced 2 years ago.
did they really revised the cap? cause my filler neck seems ok.
when i cap it back on it seems fine.
i ran into some nasty bumpy road. could this loosen the cap?

 

They did change the gas cap. At least the one they gave me for MSP13 feels different than the original. Much more solid feel, and when I take it off if feels like it was sealed, rather than just a falling off feeling like the original.

I did get a P0455 once shortly after I got the new one. After that I just pay attention when I put it on, and have not had one since.

Ken

 

Any update on this? I'm getting the P0455 and noticed reduced gas mileage on last two tanks before the light came on.

 

Anyone have tips on what to do if the plug on the tether of the replacement gas cap doesn't fit the hole? When I compared the new to the old cap, it looks like that tether plug is made of a harder plastic.