[Scoundreller]

> IMO the most practical check they actually do is the presence of a functioning gas cap.

Even that throws a code these days. 14y.o. BMW has a pump that pressurizes the fuel system to check for leaks and it’s usually the pump that breaks and throws a code.

17y.o. Corolla threw a fuel system code but it was the gas cap.

Only thing is that this pressurization check system only runs when the weather is warm enough, so resetting a code usually lets you pass e-testing as “Not Ready” because months can go by. Maybe there’s differences in summer/winter e-testing criteria.

[rootusrootus]

I don't know if it happens this way any more, but my last Subaru would do the pressurization test about 30 minutes after the car was turned off. Kinda weirded me out the first time I went into the garage and heard what sounded like something in the rear of the car inflating. Turns out that is exactly what it was doing.

[frosted-flakes]

Ford vehicles also do this.