Modern Vespa

Greetings! I am a daily rider - usually about 20 miles daily and on occasion I have to goto NYC which makes my back and forth like 70 miles. Today is first hot day of the year so far it's above 70. I filled up and rode into NYC. I noticed when I got into NYC I smelled gas more than I usually do - not sure if it was me or the other vehicles. Bike is riding fine.

Fan has come in a bunch - I am riding in NYC in traffic so that's not uncommon.

How long would y'all ride with the check engine light before getting it checked out ?? Tonight when I get home I will take gas cap off - someone told me to do this

I do not read anything unusual, except that you mention the check engine light is on, but you do not tell us when it switched on.

Anyway, if oil and coolant level are OK, and there is fuel in the tank, and the bike is riding fine and you do not hear anything funny, I expect there should not be an urgent problem.
When back home I would make an appointment to have the engine checked.

Check the battery and charging system...

A common reason for the CEL is a failed regulator giving high voltage to the battery. If this is the case fix it ASAP, as the battery gets killed PDQ under this regime.

It just came on while I was stopped at a light

Just like that? Running on idle.

JimC's suggestion is worth while.
Do you have in the board computer the function to read the battery tension?
I do not know if the GTS has that function.
My BV has that. It should read a bit above 12V with the engine off, and a bit above 14V with the engine on.

All of that language is Greek to me!! It runs fine and in the past when this happened after 24 hours or so it just went away. I am hoping keeping gas cap off over night will help.

Yes, just came on when I was sitting idle at a light. At the same time I noticed a gas smell - but am not sure if it was mine or the cars around me since I am in NYC.

Did some research
Loosened gas cap and then after a little while it just went away

Good for you.

You still have a loose gas cap !
What next ?

This never happened with my ET4

Anybody who owned an American car from the 1970s learned early on to ignore the check engine light.

Haha. Agreed. And usually I do but it just feels different when on a bike I start worrying about safety.

it's a shame that on a modern vehicles like the current gts which can show text that they don't at least show the code instead of a plain light.