Chrysler introduced the Jeep Wrangler JK series in 2007. There are several variants of the model, one of which is a four-door version, a first for a Jeep. A 3.6-liter, V-6 engine is standard, but the JK series is 5.5 inches wider than any previous Wrangler model. Troubleshooting the Wrangler JK requires some specialized tools and diagnostic equipment, but home mechanics can troubleshoot many problems.
Check fluid levels. Are there any leaks? Worn or cracked hoses, or bad seals, cause water leaks. Low engine-oil and transmission-oil levels indicate leaky seals or worn rings. Check for pools of fluids under the Jeep. Worn rings cause smoky exhaust. Water in the oil indicates a worn gasket, cracked cylinder head or cracked engine block.
Check whether it is drivable. Does the Jeep hesitate or stall? Problems with fuel pressure or the ignition cause stumbles during acceleration, or rough idling when the car is in park or neutral. On carburetor-equipped models, use a timing light to determine if the engine is timed correctly. Use the timing-degree scale on the front of the engine. A spark tester determines if each of the ignition coils is operating properly. Attach the spark tester to a spark plug wire and to a convenient ground. A bright blue flash indicates a good spark, anything else indicates a problem. Clogged fuel filters or vacuum leaks cause engine stalls. The fuel-pressure gauge indicates whether the engine is getting the fuel it needs.
Check the electrical system. Broken or poorly adjusted alternator belts, loose cables or defective alternators result in batteries that won't hold a charge. Worn or shorting wiring harnesses also cause electrical problems.
Check the steering and brake systems. A Jeep that drifts to the right or the left indicates potential damage to the steering systems. Worn ball joints, a worn steering linkage or improperly engaged steering gears cause these issues. Excessive wear on one brake pad can cause this drift to occur while braking. High-pitched squeals indicate worn front brake pads or scored rotors.
Check the Powertrain Control Module, or PCM. The PCM collects data from a number of Jeep systems. A PCM scanning tool retrieves this data and displays a code number that indicates what is wrong. The PCM scanning tool can survey several components, including the ignition, engine temperature and battery. More than 200 potential issues are stored in the PCM.
Check for engine rotation when the ignition key is turned. If the engine does not rotate, check for dead batteries or loose cables. Check if the starter motor is defective or jammed. The engine itself may have seized due to low oil levels or dirty oil.
Check if the engine will start. If the engine rotates but does not start, an empty fuel tank or defective fuel pump may not be delivering fuel to the engine. Use the compression gauge to check for low cylinder compression. A wet distributor, faulty ignition components and loose cables cause engine-starting failures.
Check the transmission-transfer case, or drive train. If the engine runs but the vehicle won't move, drive-train issues must be checked. Low transmission oil or burnt-smelling oil indicates problems with the transmission. Broken gears in the manual transmission, or faulty bands in an automatic, prevent the Jeep from moving or cause gears slips. Broken gears in a transfer case prevent the Wrangler JK from operating correctly in four-wheel drive. Broken drive shafts, axles or front and rear differential gears that are damaged prevent the Jeep from driving.
