check engine problem

I HAVE A LIGHT ON ENGINE AND THE CODE IS P0303 MISFIRE CYLINDER 3, HOW FIX THIS PROBLEM

Let the dealer look at it.

Yeah definately a dealer issue unless you''re a full blown mechanic. Try clearing the trouble code, see if it happens again. If it does, take it to the grease monkey.
 

Have you had an onstar diag?

Is yours an 06 H3????  Maybe a bad head.

I know the early year colorados had a head issue. But was fixed by late 05 early 06. i would suggest taking it into a dealer and hae them fix it.