It's a reinforcement plate/bracket to protect the fuel filler tube mainly during a rear impact (problem is the gas tank is already getting smashed at that point..but somethings better than nothing.)
YOU could be owed one of these for your 2002 ...call Chrysler with your VIN and see if your vehicle was already taken in for this by previous owner. See details below..if you just have a "brush guard" and NOT a "skid plate" you are owed this bracket...my understanding of the different of the two is strictly thickness of metal...hopefully others will chime in to comment on this and elaborate on thicknesses..
Chrysler’s Jeep Division (877) 426-5337
Mine was already installed on my 2002 when I got it.
"2002 Jeep GRAND-CHEROKEE Recall
Item Affected: FUEL SYSTEM, GASOLINE: DELIVERY HOSES, LINES/PIPING, AND FITTINGS
Date Announced: 2/4/2002
Description of Recall:
CERTAIN SPORT UTILITY VEHICLES EQUIPPED WITH A FUEL TANK BRUSH GUARD FAIL TO COMPLY WITH THE REQUIREMENTS OF FMVSS NO. 301, "FUEL SYSTEM INTEGRITY." THE ONBOARD REFUELING VAPOR RECOVERY (ORVR) CONTROL VALVE CAN BECOME DETACHED DURING A CRASH, ALLOWING FUEL LEAKAGE.
Action Needed To Fix It:
DEALERS WILL EITHER REPLACE THE FUEL TANK BRUSH GUARD WITH A SKID PLATE OR REINFORCE THE EXISTING FUEL TANK BRUSH GUARD WITH A REINFORCEMENT BRACKET. OWNER NOTIFICATION WILL BEGIN MARCH 4, 2002. OWNERS WHO TAKE THEIR VEHICLES TO AN AUTHORIZED DEALER ON AN AGREED UPON SERVICE DATE AND DO NOT RECEIVE THE FREE REMEDY WITHIN A REASONABLE TIME SHOULD CONTACT DAIMLER CHRYSLER AT 1-800-853-1403."
I personally would recommend these to all us WJ owners...if yours isn't an '02 you might get one with enough haggling with Chrysler...or check the wrecking yards and take them off '02's.. I'm sure Chrysler would charge a pretty penny for one...