A PO153 indicates a problem with the upstream O2 sensor. It isn't responding properly (or too slowly). This sensor only starts working when the engine has warmed up, so that is why it may have taken a while to come on. What I recommend is to check the wiring to it. It is located on the exhaust manifold. If the wiring is good, chances are the sensor just needs replaced.
Let me know what you find or if you have other questions.
Wednesday, December 29th, 2010 AT 12:46 AM