Jeep O2 Problem from Leaky Exhaust

How to find a Problem on a 2008 Jeep Cherokee 3.7L with a Check Engine light on and a P013C. The vehicle owner went to the Jeep dealer and was charged for an Oxygen (O2) sensor that did NOT fix the vehicle. We diagnosed and tested the Jeep finding the root cause of the problem. We found the real problem. We TEST Not Guess!