CEL already :(
 

After just 500 miles I've now got a persistent check engine light that comes on as soon as I start the car and stays on.

After some quick googling I checked the gas cap and it was loose, so I tightened it and restarted the engine several times but with no change.

Any other easy ideas before I take it to the dealer?

Did you take it for a short drive after tightening the gas cap. It usually takes the car a minute to clear the CEL in some cases.

Take it to regular auto parts store like Autozone or Advance for a free reading if the dealer won't take you right away. Likely something dumb/minor that will be fixed no questions under warranty. May just require a reset and never come back.

You need to drive it a bit before the CEL clears. Restarting the engine won't do it.

If its just gas cap being loose you just drive it until the light goes away.

Might take a bit, i had it happen on my BMW once. Couldnt actually tell if it was gas cap related but it was one of the first things i did (retighten gas cap) and it eventually went away.

I just drove it about a mile stopped/restarted the car then another mile back and it's still there :(

Do I need to drive it more? Or are there any other simple/silly reasons for the CEL I could look at?

Yeah you need to drive at least 30 minutes, and it can be as long as a hundred or so miles.

It really depends on the driving conditions it wants to see for whatever code was set. Read the code yourself, or go to a parts store to get it read. If it was the gas cap, then it's likely an evap system code(maybe P0457). If it's something else, then off to the dealer you go. There's a chance that by the time you get to the parts store, the light may go out.

if it hasn't blown up, i wouldn't worry about it.

A suggestion for the future, order an obd dongle and get a free app (torque lite?) to see what codes you may have and it should allow you to clear codes to see if it comes back. Cheapest option to checking your own.

This. Get a code reader, they’re so cheap now there’s no real excuse to not have one if you’re into cars in any capacity whatsoever.

it is almost easier to just drive down to the autoparts stores to get it read.

they do it for free, and if there's a problem, you can get the part immediately. so on my timeline, i can install that part in 5-6 months.

i have one, and i barely ever use it. usually only think of it when i'm driving by a auto parts store, so i just stop in and let them scan it.

If you have plans to own a car built after ~2005 or so for the foreseeable future, and are a DIY kind of a person, a $20 code reader from Amazon (or any place) will be one of those things you will use constantly out of your toolbox.

Think of it like a torque wrench. Or spark plug socket. At some point you'll just need this handy, even if you only use it once a year.

1996. OBD2 has been around for a long time now.