OBD Code :139

Have you ever wondered what these codes mean? Well ya we  never wonder until that damn check engine light comes on. And thats exactly what happened to me. Was happily driving around when that light came on. And since then its been on my mind like an unsolved mystery. Took it to few places where they do this "Free check engine diagonistics" and I got this code 139. Did some reading up but led me to no where. And to get this thing repaired most places charge like $99 for their diagnostics and then additionally for the parts and labor and what not. Not to forget that they will list down an additional 100 other things which can be repaired on your car with a 4 digit bill :) i feel that  going to a car mechanic is like going to a dentist. You go there for one issue and you end up knowing that you have many many more and the best part is that all the work is really cheap ;) And just when you do everything you can to save some money...some thing like this happens and then really makes you wonder....Why bother saving???? Shouldnt we just live for today???