Your Jeep's Electronic Control Module (ECM) creates and stores error codes when a fault occurs in the mechanical or electrical system. Once you've corrected the problem, removing the code is important. The steps differ depending on the age of your Jeep but are all relatively simple. If you've cleared the codes and the check engine lights persistently comes on, check for new error codes.
Allow the Jeep to run after undergoing repair. The ECM resets itself after a number of successful ignitions that proves the fault is no longer present.
Disconnect the battery cables. With some Jeep models you only need to do this for a few minutes; with others, leaving the battery disconnected overnight is beneficial. According to go.jeep-xj.info, 1991 to 1997 models require overnight disconnection, whereas 1984 to 1986 models need a couple of seconds of disconnection. Try both to find what works for your jeep.
Start the ignition. Drive forward for a few feet, then drive in reverse for a few feet. Turn the ignition off. This method works for some Chrysler models, according to Sid Willoughby at Allpar.com.
Clear the codes with a SCAN tool. Connect the SCAN tool to the Assembly Line Data Link (ALDL), usually found under the dash. After the SCAN tool reads the engines codes, it gives you the option to clear them. A tech at your local auto parts store will do this for you free of charge if you don't own a SCAN tool.
