Fuel cap pressure is a standalone test, and if you fail it, yes, you fail the entire test and have to go through the whole emission inspection/test procedure again.

If the fuel cap fails the gasket is the most likely culprit, so you don't need to buy a new cap - maybe just a gasket. The internal pressure and vacuum relieve valves in the cap rarely fail, but the gasket wears, and test errors are not unknown.

If your fuel cap fits snuggly on the filler neck and the gasket appears undamaged to visual inspection, it is probably okay.

A couple of tests ago my fuel cap failed the test. I asked the tech to remove and reinstall the adapter and cap on the tester and retest it. He did. It passed, and no problems since.

Seems to me that a failure should automatically require and immediate verfication that the test adapter and cap are properly secured to the tester and a retest, but I guess that's not what they teach these guys in emission tech school. A big DUHHHHH!!!

In my time as an aerospace test engineer, if a test failed the first thing we did was a complete verification of the test setup and rerun the test, but what do I know?

Duke