Hi, just picked up an 02 4x4 qc sport with 5.9l,of course 3 weeks later it threw a p0138 code.Can someone tell me if this is the o2 sensor between engine and cat or the one after the cat?Also my mpg is 9.1 city, is this within normal range or do i possibley have a fuel/air ratio or plugged cat problem related to p0138 code?I didn't expect great mileage but if it can be improved I won't complain.Would sure appreciate any help I can get.

 

I BELIEVE THE 02S YOU WANT IS THE LEFT BANK PRE-CAT O2S. IT IS SHORTED IF I AM NOT MISTAKEN. I WOULDNT THINK THAT YOUR CAT ISNT CLOGGED DUE TO THIS. IF THERE WAS A PROBLEM WITH THE CAT YOU WOULD ALSO HAVE A P0420 CATYLST EFFICENCY CODE AS WELL. AS FOR THE 9.1 MPG I MAY IMPROVE WITH THE REPLACEMENT OF THE O2S BUT THE BEST BET IS JUST TO DRIVE CONSERVATIVE. READ THE MODS IN MY SIGNATURE. BEFORE THE SUPERCHARGER I WAS GETTING 12.1 MPG WITH THE LIFT KIT AND TIRES WITH THE SUPERCHARGER I AM PULLING ABOUT 17 MPG.

P.S YOU COULD ALSO BE HAVING AND EGR PROBLEM THAT IS REFLECTING IN THE 02S BE SURE TO CHECK THAT AS WELL.

 

Thanks! atlaticblueram, I'll replace sensor for now and see if there is any improvement.As for mods, that sounds great, but that will need to wait for cash flow and wife's OK.Much appreciated.