First thing to do is take off your gas cap and make sure it is on correct and sealed tight. Next take it to any autoparts store as tell them your CEL is on and you would like to pull the code. This is free and they may just hand you the OBD-II code reader and have you read the code yourself. The OBD-II port in underneath the dash on on the left side of the drivers side. Just in case you are unfamiliar with what it looks like below is a picture. Picture is not of the Clarity's but the port looks the same and is in the same general area. Record the 5 alphanumric code (that will most likely start with the letter "P") and post it in this thread and we will help you figure it out.
Didn't Honda include a loose gas cap light? Better than my 2011 outback. Recently, on a long trip we go engine, emergency brake, cruise and VSA lights all on at the same time. It was a loose gas cap that was in fact tight so I replaced it just in case ($10). Apparently Subaru believes they have to turn all lights on for you... Now I carry a OBD-II tester just in case... (Amazon - about $20)
The Clarity has some issue with public charges, voltage fluctuations or something. Did it stop charging partway through? If you have a loose gas cap it sets off its own information message "Tighten fuel cap" or something. I had it and it is annoying. After tightening gas cap several times it finally went away. I think it took a certain number of starts actually (so don't worry if that message stays up after tightening fuel cap). Many check engine lights go away on their own as they are just something reading out of range temporarily, but they should be checked to see if it is important or not. If you don't want to go to the Honda dealer, stop by the parts store as AnthonyW suggests, come back here and report the code. Or just take it to Honda dealer. As a test, stop the car, start it again and see if it is still there. Maybe repeat a couple times, it might just show for 3 starts or something like the tighten fuel cap message. It will still be stored in memory so the dealer should be able to pull it still.
I’ve had that happen 3 times at public chargers, that I think had some malfunction. If that’s the case it’ll go away in a few hours.
This is one I use with the Clarity PHEV Android and Torque Pro: https://amzn.to/2JXesUw For my BMW i3 for coding it I use this Wi-Fi model: https://amzn.to/2LwKn3W If you use an Apple phone, make sure you get a compatible model. I think that Wi-Fi one is, but look at any code reading App and see what they recommend.
@AnthonyW is working with ScanGauge as a beta tester to get all the PIDs that will access the incredibly large amount of unique info regeistered by our Claritys. If you don’t want to wait until that’s done, I’d make sure to get one that’s compatible with ScanGauge because it looks like they will be the first to come out with a Clarity specific interface. Current OBD II readers don’t yield hardly any Clarity specific info. Check out his post. https://www.insideevsforum.com/community/index.php?threads/scangauge-ii-extended-pids-capacity-and-specific-energy.2633/
With AnthonyW working with the ScanGauge II people, it would seem there's no other choice. https://www.insideevsforum.com/community/index.php?threads/scangauge-ii-extended-pids-capacity-and-specific-energy.2633/
No need for a ScanGauge for reading and resetting MIL (check engine light), a cheap standalone ( https://amzn.to/2LBQIKD ) or BT/Wi-Fi code reader can be had for $20 or less. PS I agree, a ScanGauge might be nice if you want to do deeper analysis, but this thread was related to reading/resetting the codes when the MIL lights up.
When I got gas last night, after driving 200 miles, the light went off. Maybe it was gas cap, although I tightened it after someone recommended. So we will see.