Hyundai Repair: Check Engine Light, hyunadi, exaust manifold

Question
I have a 2001 Hyunadi Accent that has never given me any problems until now. I took it in for the 90,000 mile tune up a couple months ago, at which time the check engine light had just come on. They replaced the exaust manifold which had 4 cracks in it, along with the O2 sensor, as that was the code the machine was kicking out. A couple days later, the check engine light came on again, giving the same code. They replaced the O2 sensor again, thinking I had just gottena faulty one. However, since then my car has been giving out the very same code, and they can't find anything wrong. They have checked all of the wiring, replaced the sensor, and less than a hundred miles later, once again the light comes back on. It is giving code P0133 and I can't find anywhere online that will tell me if there is anything I can get done myself, or rather by my dad or boyfriend as I am not car savvy. This is becomming incredibly annoying, and I do not have the time to keep running in and out of the shop. Is there anything else I can do?

THanks
Corey

Answer
The most frequent cause of code P0133 on your vehicle is a leak in the front exhaust pipe.  The leaks usually occur in the flexible part of the pipe.  Even a small leak is sufficient to lead to this code.  Check very carefully for leaks in the front exhaust pipe and replace the pipe if it's leaking.