This is a pretty straight forward code pointing to a fault in the Throttle Position Sensor. Replacing this sensor should solve the problem. The TPS is mounted to the throttle body.
Remove TPS mounting screws.
The throttle shaft end of throttle body slides into a socket in the TPS. The TPS must be installed so that it can be rotated a few degrees. (If sensor will not rotate, install sensor with throttle shaft on other side of socket tangs). The TPS will be under slight tension when rotated.
Ok. The next step is to check the wire harnes from the TPS to the PCM for broken wires, or rubbed through wires grounding out. Also check all the fuses. If the wire harness and fuses look good, then unfortunately, the problem is going to be internal of the PCM. Also- make sure the installtion ws lined up correctly (see install procedure above). If the "tangs" are not lined correctly, this code will set.
Here is JEEP's official diagnostic of the P0123: