Here is the short version of my story. My teenage son complained of his check engine light on.  Knowing that it would be at least $100.00 to take his car to the shop, I purchased the Actron CP9135.  In no time it said the vehicle had had 4 random misfires in the cylinders.  Knowing this was rather unusual, I asked my son if he had run his car out of gas.  Bingo! Problem diagnosed.  I cleared the codes,and the car is running fine.  Well worth the money.