Check engine code 42?

A few weeks before the engine light came on, I heard some sort of exhaust issue or something happening. I have attempted to patch a hole in the muffler. After the code came on and the first couple of days it would die while stopped and then that stopped. Now when I drive the engine is puttering, and when you push the gas, there is a hesitation, but the truck has not been dying. The check engine light seems to be illuminating at different brightness. The truck starts normally. The book that comes with OBD one reader says that it’s either 1- electronic spark timing, circuit open or shorted or 2-direct ignition system bypass circuit open or shorted to ground during Engine run or 3- fuel cut off relay circuit open or shorted to ground. Any advice on how or what to test?