The check engine or service light on a Jeep is a warning sign something is wrong with the engine. A problem with the computerised engine-management system will trigger a fault code and cause the "check engine" light to come on. Address the problem, then reset the light to make sure you've resolved what tripped the code. There are several methods for resetting the light.
Disconnect your battery cables from the battery posts with a 6-pt. closed wrench in the size appropriate for the battery bolts. Remove the negative (black) cable first. Leave the battery disconnected for several minutes, according to Allpar.com. Reconnect, this time starting with the positive cable, and crank the engine. The code should be gone.
Crank the Jeep. Drive it forward, then backwards, and shut off. Repeat this procedure three times. The codes should clear on the fourth crank.
Use a OBDl or OBDll scan tool. Plug the tool into your Jeep's ALDL (Assembly Line Diagnostic Link), a small, rectangular electrical port usually located under the dash. Turn the key to the "on" position. Scan the computer for codes and select the option to clear the codes.
Wait for the code to clear itself automatically. Once the component is fixed, the check engine light disappears after several successful ignitions. The code is then stored for a while. If the engine continues to start and run without a reoccurrence of the original problem, the code is wiped out.
You may not have fixed the problem if the code keeps reappearing. Loose gas caps have been known to cause check engine codes, without anything being wrong with the engine.
Don't disconnect the red battery cable first. You risk electric shock.