so i have a 97 with a 5.2 318 4x4 auto tranny and it keeps throwing a p0138, so i replaced the o2 sensor before the cat which helped my gas milliage alot but yet agian i am getting the p0138 code today so what should i do? should i get the other sensor or what?

 

That code is for the downstream o2, not the precat sensor.