The plug is under the dash on the driver side.
You will need a code retrieval tool available at the auto parts store, plug into the OBDII port by the base of the steering wheel and it will tell you what the fault codes are.
Drain plug is hex 17mm; fill plug is hex 13mm
.035
.035"
Look for a loose plug, or plug wire.
4cyl is .035
.035 inch
.035 in GAP
.035 inch
The 2002 Jeep Wrangler OBD 2 port is below instrument panel, left of brake pedal
they are located on either side of the block
.035