The Jeep power train control module (PCM)--or computer, as it is known in layman's terms--controls the vehicle's ignition, emission and fuel systems, along with other auxiliary systems necessary to the operation of the drive train. When the PCM detects a malfunction in the drive train or related systems, it will generate a trouble code that will remain until the problem is corrected or the code is cleared. In extreme cases, hard codes are generated, which can only be cleared with a proper scan tool, or by resetting the computer.
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Things you need
- Scan tool or battery terminal wrench
Connect the scan tool's data cable to the data link connector (DLC) port. In most Jeeps, the DLC port is located next to the fuse panel under the driver's side dash.
Refer to the scan tool's specific owner's manual on how to run a self test on the PCM and clear the code. There are certain emissions-related codes that may require a Chrysler/Jeep dealership to inspect and clear. Disconnect the scan tool from the DTC port when done. If you do not have a quality scan tool, refer to Step 3.
Disconnect the negative battery cable and leave it disconnected overnight. Reconnect the negative battery cable in the morning and all but any hard codes will be cleared. By disconnecting the battery, you are essentially giving the computer a form of amnesia, whereby the computer forgets any stored codes. However, if you have not corrected the problem that caused the code in the first place, the code will return soon and the "check engine" light will come back on.
Tips and warnings
- All scan tools are not created equal. The ones used in most dealerships cost anywhere from a few thousand dollars on up to nearly £13,000. When purchasing an aftermarket scan tool, be sure the device has the options you want, as well as the ability to work with your particular vehicle.