Ok so your running lean... this meains you have too much air, or not enough fuel exiting the combustion chamber. There are two ways that you could be receiving a false reading and thus a false CEL... if you have a crack anywhere in your exhaust system between the O2 sensor and the engine or, the sensor is bad. If you are 100% sure that you checked arround your collector, and around each pipe for cracks and there isn't one... then you have the posibility of a bad sensor, or your not getting enough fuel into the combustion chamber.
Not enough fuel can be caused by a failing fuel pump, a clogged fuel filter, faulty/dirty/clogged injector(s). Either of these will give you a lean condition every time. If your exhaust checks out, I would HIGHLY recomend replacing the fuel filter, if that doesn't work, you will need to run a fuel pressure test. This can be done with a rental fuel pressure test kit from Autozone, Advance Auto Parts, etc... Connect the fuel pressure tester to the fuel rail and see what you are reading and compare that to average operating PSI of our motors.
I would start with an extremely thurough inspection of the exhaust manifold, then consider replacing the fuel filter, then consider a fuel pressure test... If all of those lead nowhere, then replace the sensor. I say replace the sensor last because it's the most expensive.
1. Check exhaust system 100% between O2 sensor and block. (FREE)
2. Replace fuel filter and re-check trouble codes... (~$15.00)
3. Rent fuel pressure tester and verify fuel system performance (Rental..l FREE)
4. Replace O2 sensor if the above 3 turn up alright... (~$50+)
IMHO, those are the steps I would start with to diagnose a lean condition with the jeep still functioning symptomless.