O2 sensor location and associated codes

[kmcdonough]

Recently my MIL came on. My scanner detected the DTC's P0137 and P0138. From what info I found, it looks like those DTC's pertain to the Bank 1 sensor #2. I changed that sensor last night and today I cleared the codes and took the truck for a test drive. The MIL came back immediately. I drove the truck about 10 miles in total, turning it off and re-starting it twice. The MIL stayed lit. When I got home I hooked up the scanner and got the same two codes. My first question is am I correct in assuming the 137/38 codes are associated with the #2 sensor? My next question pertains to the location of that sensor. Looking under the truck, from front to rear, I believe the order on the exhaust is the CAT, then DPF, then muffler. Is this correct? I changed the sensor between the cat and DPF. Is this the #2 sensor? There was also a smaller what looked to be sensor in both the Cat and DPF. What are these? I am right at 67,000 miles and am about to do the CCV/EGR service. Although I cant find any info stating so, could this be a cause for the DTC's? Any help would be appreciated. Thanks in advance.
Kevin

 

[sag2]

Since you have access to a scanner, clear the codes. Then unplug one sensor at a time and note the code you get for each sensor. The code should set immediately so it should give you the accurate descriptions and locations for each sensor. Then you can continue diagnosis knowing exactly what sensor(s) are involved.