This has been going on for about 2 months know. I've changed the rear heated o2 sensor twice, and yet the code comes back, even after clearing it several times. I was told that it could be either the thermostat, egr valve, maf sensor, electrical problem, and that its burning rich feul. ive had enuff with this car, and i really dont want to start throwing $$ around. Since i dont have to pay for labor........but i dont want to waste time!! I might take it to the dealership tomorrow to have it diagnosed.

 

bump.........

 

The downstream O2 sensor monitors the condition of the cat. If your constantly getting an error code for that O2 and the circuit checks out ok, you probably have a bad cat.