Hello,
I have a 98 xj, p0138 and p0141 for the O2 sensors keep causing the engine light to come on.

The Catalytic converter was rusted off, so I changed that. Changed both O2 sensors with NTK or NGK brand (whichever was the OEM) as one of the previous ones were Bosch and the other was just old. Jeep has ~95k on the engine, ~135k on the bottom. 4.0L, auto. I've also changed the IAC


So, what should I be looking for? Bad wires? I need to get it fixed so I stop getting 15 mpg, lol.... I was getting 19-20 a while ago.

Any suggestions are appreciated.

 

There's a fuse in the PDC. Maybe blown?

 

Does this have California or Federal Emissions? The PCM's are programmed differently and if you have miss matched components or inferior components it will cause the O2 codes to appear erroneously.

 

Examine the O2S harness looms. In the engine bay the upstream O2S harness comes out of the fuel injector wiring box on the left side of the engine and passes over the intake manifold; sometimes the O2S harness chafs at this point. Examine the downstream harness for damage, Occasionally a harness will rub on the drive shaft.

It's good that you installed new NTK O2S's in both positions. Sometimes an old upstram O2S with a new downstream O2S will cause problems.

Here's an image that shows the location of the O2S heaters fuse in your PDC. There have been many cases of this fuse blowing. As bobvalli said, it may be blown.