OBD II check engine codes warn drivers of many types of engine problems and are a standard system in all cars made after 1996. The Jeep code P0122 warns of an issue with the throttle sensor.
The "P" that appears in P0122 refers to a powertrain issue, the following "0" means it's an issue that isn't Jeep specific---it's a Chrysler-wide issue--- and the "1" that comes next means that this is an issue with the emission management system.
An OBD II scanner that comes across a Jeep P0122 code should give the readout: "Throttle/Pedal Position Sensor/Switch A Circuit Low Input." This means that your Jeep's computer has detected a low voltage below the acceptable range, probably lower than between 0.17 to 0.20 volts in your Throttle Position Sensor.
A TPS not providing enough voltage may be caused by a faulty sensor or wiring or, if recently replaced, it may be improperly adjusted. Check with a trained mechanic to see if you need to replace your TPS. A replacement TPS is not a major investment, and can usually be purchased for much less than $100.
Driving with an improperly adjusted or faulty TPS could be dangerous for drivers as your Jeep could exhibit erratic or no acceleration, stalling problems or throttle surging. See a mechanic as soon as possible.
