I just went to the dealer and they tell me the CEL will go on if I put on a locking cap.
Good grief!
Stant and others have been making sealed fuel system caps (locking) from the beginning of sealed (non-vented) systems.
The system on the Cruze has not changed from 2011.
The only thing that should be considered is, IF a check engine light was set, AND it was a fuel system integrity test, AND the cap failed the vacuum test, it would not be a covered repair.
But that is only because the part was not supplied, as original equipment, by Chevrolet.
So, get a aftermarket cap from Stant, and try it out. I'm confident it'll be fine, but if it did set a light, put the original cap back on and the light will reset after about ten start/run cycles if it was caused by the cap.
If the light goes out, return the cap for credit.
I have never had a CEL caused by a locking cap.....I have had CEL's from, lose caps, or folks refuelling while the engine is running, or caps that won't hold vacuum......locking type or not.
The dealer is the last place to ask about anything not installed on the car by the manufacturer......they will always recommend against it because they have no information available.
Myself, I don't like them because sometimes the lock freezes here in the snowbelt and then you have to get the car somewhere warm to get the cap off.
You however, may be operating where that is of no concern.
Rob