I35 - Service Engine Soon light?

[port80]

Hi,I have I35, 83,000KM on it.Last week I saw Service Engine Soon light.I took it to dealer/mechanic (from whom I bought) after 3-4 days and he attached a device to check and see if any sensor not working.

While checking, the light gone and he told me that it is saved on local computer and I don't need to worry and just drive it.

Today light light appears again, after running 400 KMs

I am making sure that gass cap is tight and turn at least 3 to 6 times.

Also noticed that when I open cap for filling up gass I see rusty metal surface inside. Not sure if that matter?Could it be bad gass cap?

Any idea/help?thanks.

[Markc]

The same thing was happening to me off & on. I too noticed rust and a non smooth surface on the filler neck where the gas cap seals. I stuffed a rag in and went at it with Scotch Brite, (you don't want the possiblity of a spark). I wiped it down with rust check and also wiped the risidual rust off the o ring on the cap. That was only half a tank ago, so only time will tell. The code I was getting was PO456 which is minor evaporative emmission leak or something like that.

[MinisterofDOOM]

Definitely possible for a bad gas cap to cause it. That'd be my first try after making sure the cap and car seal surfaces are clean.