Error codes or diagnostic trouble codes (DTCs) occur on vehicles when a sensor or component fails its intended function or fails to communicate to the computer. The computer then trips the malfunction indicator light (MIL) and displays a check engine symbol on the instrument panel. To effectively reset the error code, the problem must first be diagnosed and corrected, if applicable, to keep the MIL from re-tripping. Simply clearing engine error codes on a Jeep Grand Cherokee will not fix the underlying problem. There are two procedures to clear error codes.
Open the driver's door on the Jeep Grand Cherokee and locate the diagnostic link connector under the dashboard. It is to the left of the steering wheel, uncovered and shaped like a trapezoid.
Plug the OBD II scanner into the connector and then turn the ignition key to the power accessory position. This will illuminate all the warning lights on the instrument panel without the engine running.
Refer to the operation manual of the scanner. Because so many companies make them, the operation of your specific scanner will be detailed in the manual. On a whole, running these scanners is easy and almost self-explanatory.
Scroll to the "erase codes" option displayed on the on-screen menu. Some scanners also feature an erase button option. If so, press erase. If you had to scroll to the option, press the "enter" or "send" button. Some scanners may ask if you're sure you want to erase the codes. If so, select "yes."
Watch the display screen of the scanner until it reads "command sent" and then start the engine to the Grand Cherokee. Check the instrument panel to ensure the error code has successfully been erased and the MIL is no longer illuminated.
Open the bonnet to the Grand Cherokee.
Use a wrench to loosen the negative battery terminal clamp's retaining bolt and nut.
Use a pair of Channel Lock pliers to twist the loosened terminal clamp and lift it off of the battery terminal.
Turn the headlight switch on and the ignition key to the accessory power position. This will expel any stored charge in the electrical system and wipe out the computer's memory. Wait 10 minutes.
Turn off the ignition key and the headlight switch and then reconnect the negative battery terminal clamp. Start the engine to ensure the error code is erased and the MIL is no longer illuminated.
While you can erase codes on OBD II Grand Cherokees by following Section 2 without using a scanner, it is not recommended on later models. Most all newer vehicles come with theft-prevention radios and internal alarm systems. Once the memory of the computer is wiped out, the vehicle will go into protection mode and also wipe out the radio and internal alarm systems, making them both inoperable. While they can be reprogrammed, obtaining the information will have to come from a Jeep dealership and will incur cost. Most all parts stores will read and offer to erase codes for you; although in some states, they are not allowed to erase codes, but may allow you to press the erase option on the scanner. Once the computer error codes are erased, the computer needs to rediagnose itself. It will relearn and recommunicate with all the sensors and circuits integrated to the system. This may take several normal driving cycles for the computer to communicate with all the sensors and circuits until it is in readiness mode. It is at this point where the computer will re-trip the MIL if it detects the repair was not made to the Grand Cherokee. Clearing the codes to fool emissions testing will not work. Equipment attached to the vehicle will be able to tell if the computer is in its readiness mode and will fail it until it is ready and the MIL remains out.