I currently have two codes in. One is 0503 and the other is 0303. Front right and left heated O2 sensors... Why are these both coming in at the same time??? I do not know where these are located so any help would be cool. Also where can I get them and how much are they??? Thanks

 

They are located on the y-pipe. There is one for each pipe coming down from either side of the engine.

I had these exact same codes one time, you may want to try resetting the ECU before you go out and buy some new O2s. I had these codes way back in late June 2004, and I reset the ECU and they haven't come back since.