SES light on-- Injectors?

[trailguide2u]

Truck runs fine but light will not shut off. I tried disconnecting the battery for about a hour. I cleaned the Amsoil filter (dirty). The truck maybe smoking slighty more. I did notice that the coolant has dropped some over the 3 years I have had it. Some loss I figured was evaporation. I do have a friend at a local chevy dealership that will check the code for free----thankfully..
Any thoughts??? I do realize anything is possible.

Happy Turkey Day

[Kennedy]

You are going to have to have the codes scanned. I doubt that it is injectors as they seldom set codes, and typically exhibit plenty of symptom when they go.

Did you just start using your block heater?