Check Engine Light on cng

Not sure what you mean cng, but if you are talking about your check engine light on your car it means, you need to go to a car repair shop(the type you have if possible) and they'll put it on a computer that tells what is wrong. Can be a lot of things!!First you can see if you have enough oil in your car, and check all the fluids. But after that it could be a lot of things, from a missing fuse(under $1 to fix up to worst case , a cracked engine- which might not be worth fixing)

If you have an oxygen sensor in your vehicle running on cng can trigger that which causes your check engine light to come on.