How to Troubleshoot the Jeep Grand Cherokee's Engine Light

by Richard Ristow
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Car dashboard image by Andrejs Pidjass from

Once a Jeep Grand Cherokee's check engine light illuminates, it means the On-Board Diagnostic system has repeatedly detected an engine malfunction. A problem has to repeat itself several times before the Grand Cherokee's On-Board Diagnostic system will give it a "fault" status. There are ways to troubleshoot the system, and that involves examining the fault codes. How to do that depends on the year the Grand Cherokee was manufactured.

Grand Cherokees 1996 and Later

Step 1

Open the driver's side door and plug your OBD-II scanner's cable into the Grand Cherokee's diagnostic outlet. This Data Link Connection will be located on the driver's sidde of the Jeep, beneath the steering wheel, somewhere between the left kick a panel and the gas pedal.

Step 2

Turn the Jeep Grand Cherokee's electrical system on. You may have to also crank the engine, depending on the brand and type of OBD-II scanner you own. At this time, if you do not have a self-starting scanner, you will have to switch it on yourself. The procedure for operating a diagnostic scanner varies by brand, and it is always best to defer to the exact instructions contained in your scanner's user manual.

Step 3

Look at your scanner's screen. If your brand of hand-held is not preprogrammed to retrieve diagnostic codes, you will have to key a "scan" command. Some scanners have a dedicated button for this, and others require you interacting with menus.

Step 4

Reference your manual for the codes that come up. You will need to differentiate between what is a "pending" code, and what is a "fault" or "trouble." Fault codes trigger the check engine light, and pending codes do not.

Step 5

Reference Chrysler's supplemental OBD-II codes online (See Resources). Your scanner's handbook will likely only have the generic OBD-II codes universal to all cars and light trucks after 1996. Once you have found all the definitions for the fault codes reported by your scanner, you can make an educated decision on whether to do the repairs yourself, or consult a professional mechanic.

Jeep Grand Cherokees Before 1996

Step 1

Get behind the Grand Cherokee's wheel and slide your key into the ignition. Turn the key in the following pattern: On-Off-On-Off-On. You need to do this in 5 seconds or less for the Grand Cherokee's computer to recognize it as a command.

Step 2

Grab a pen and paper and count the number times the check engine light flashes at you. It will be a code. Long pauses will be used to separate fault codes. The codes themselves are two digits. The first number will flash. There will then be a pause before the second number flashes. For instance, code 41 will be represented by four flashes, a pause, and then one pause.

Step 3

Look up the Chrysler's flash codes online (See References). Since the Grand Cherokee's diagnostic system predates Environmental Protection Agency standardization, other manufacturer's codes will not help. Once you have found definitions for the flash codes reported to you, you can figure out whether to take the Jeep to a garage.

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