"check engine" light

[tmleadr03]

It is a new thing all the cool kids are doing these days.

It pressurizes the system and measures the drop of pressure. A large amount o pressure drop means it is most likely the gas cap since otherwise it would be a small hole elsewhere in the system. So a slower pressure drop. More of an educated guess then a "known" variable.

I hope you not in some way blaming me for your "Check engine light" I didn't ask you to stick your hose thingy down the filler.

Serious note I have this feeling it is a coincidence. If you look at the filler / line down to the tank if you see wires to a sensor then maybe but I have never seen a sensor in that area. Newer cars do tell you if you need to replace your gas cap. Wife's 2008 Commander (the one I was trying to transfer the gas out) did it to us, it has a dedicated idiot light that lite up and said "check engine gas cap." sure as shit simple fix. I believe the fuel system is closed loop and somewhere there is a sensor that tells the computer it has a pressure leak and figures it is the gas cap. Not sure how it knows it is that or a leak with the carbon canister or lines.

How far have you gotten to figure it out?

Formatting error being blamed on posting from cell phone.