Armchair mechanic here, and having a devil of a time with an O2 sensor on my daugher's '04 WJ Laredo 4.0L 6-cyl. w/ 138,000 miles. The history is that we had some O2 sensor codes (don't recall all of them now), and poor mileage. Her boyfriend replaced all 4. Unfortunately, he didn't secure the wires on the 2/1 sensor (front, after mini-cat if I'm correct), and the insulation melted against the exhaust pipe, and it shorted, causing the fuse to blow (found out about the melted wire only after blowing a second fuse).
On the 2/2 sensor, the replacement was a allegedly a OEM-type, but the alignment tabs on the male/female connectors didn't align, so they were filed down on the sensor-side connector. When all of this was done, and codes cleared (plus PCM reset via battery disconnect), I was getting a recurring P0158 code. Thinking I had a bad sensor, I replaced this one again and cleared the code. It would stay off for the duration of the initial trip (whether 1 mile, or 100 miles), then the MIL comes on and the code is set again (always the same P0158).
Well the code says that sensor may be shorted to voltage, so I thought perhaps a the O2 sensor relay - so I swapped with the (same part number) horn relay, but no change. I should also say that I checked the wire-loom around the top/back of the engine by the firewall, and did find the loom starting to disintegrate, but it appeared all wires in-tact. I cleaned this up with some new loom, and put some silicon super-tape over the offending engine bolt.
I'm now at somewhat of a loss, and could use some help. From here I'm thinking I could begin tracing wires or try yet another sensor (would go Mopar part this time vs. Bosch). I'm also wondering if this could be a legitimate code in the event of a bad mini-cat, injector, etc. (high-voltage indicating running very rich?). I guess last-resort would be to take it to the stealership and take my lumps, but need to do something soon as emission inspection is due.
Thanks in advance for any help you guys can offer.