I have a 2003 with the 3.0. Engine light on, P0431 warm up cat efficiency below thresh hold. I am a mechanic but never played too much with diagnostics simply because I dont have the patience. Has anyone had this problem and if so what fixed it? I am trying to go low cost and avoid a dealer.

Thanks

 

More than likely it is the LH Precat, or that O2 Sensor.