Truck Repair: check engine light, gas cap, time problem

Question
gmc 2003 sierra 1500..has been in shop twice...once for carbon cleaning due to gas cap not on tight enough? secong time  problem with fuel line...light is on again within 2 days. before I take it back to the dealer I would like  a little more info as to waht could cause the problem and what really should be done to find the problem and fix it.

Answer
Hello Melany,
You have a question mark after carbon cleaning.
Does that mean you wonder about that?

Me too.

I assume if your light came on, you took it right in, correct? The gas cap loose will cause the light to come on, but if you didn't run it for an extended period loose, like several thousand miles, I doubt any carbon was formed due to it.

I can think of NO fuel line problem that would make the light come on.

So my thought is they never found a problem, just repaired something that may not have been a real problem, and cleared the codes.

Have them at least tell you what code or codes they are finding. Surely they are connecting a tool and reading the codes.

That should also all be under warranty.

Van