All of the OBD-II engine sensors can be tested for proper functions. Test any suspect sensors. Test the O2 sensors, inspect the O2 sensor fuses, and test/inspect the O2 sensor wire plugs and O2 wire harnesses for corrosion, damage, and short or open circuits. Inspect the speedometer drive on the transfer case, and the related wire plugs and wire harness.
If you buy a new engine sensor, get a genuine Jeep part. Most auto parts stores sell cheap crappy Chinese "Lifetime Warranty" parts that are poorly manufactured from inferior materials and are often out of specification, or even failed, right out of the box. The ones that aren't faulty often have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts. Buy good quality repair parts and genuine Jeep sensors for best results.