01
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Frame & Unibody Rust / Rot
The Problem
Early TJs are notorious for frame rust, especially at the rear frame rails, crossmembers, and body mount areas. Salt-belt vehicles often have severe rot by 100k miles.
The Fix
Wire-brush and treat light rust with POR-15 or Rust Encapsulator. Severely rusted sections require frame welding or section replacement. Full frame replacements are available from Rock Auto or aftermarket suppliers.
DIY
$50–$400
Shop
$800–$3,500+
02
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Death Wobble (Front Axle / Steering)
The Problem
A violent, uncontrollable shaking of the front end at highway speeds (usually triggered above 45 mph). Caused by worn track bar bushings, ball joints, tie rod ends, or loose wheel bearing.
The Fix
Inspect and replace track bar and its bushing first—this is the #1 cause. Then check front ball joints, tie rod ends, wheel bearings, and steering stabilizer. A complete front-end rebuild with aftermarket heavy-duty parts eliminates it for good.
DIY
$150–$350
Shop
$400–$1,200
03
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Radiator Cracking / Overheating
The Problem
The factory plastic-tank aluminum radiators crack at the seams, especially on 4.0L engines. Overheating can cause head gasket failure or worse.
The Fix
Replace with a 2-row or 3-row all-aluminum aftermarket radiator (Mishimoto, CSF, or similar). Also flush and replace coolant, inspect the thermostat (195°F recommended), and check the water pump while you're in there.
DIY
$100–$250
Shop
$300–$600
04
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Soft Top Leaks & Zipper Failure
The Problem
Factory soft tops develop leaks at seams and zippers within a few years. The plastic rear windows also yellow and crack with age, reducing visibility.
The Fix
Apply 303 Fabric Guard and a zipper lubricant (no WD-40) for minor leaks. For failed tops, replace with an aftermarket top from Bestop or Smittybilt. DIY install takes about 2–3 hours with basic hand tools.
DIY
$50–$450
Shop
$500–$800
05
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AX-5 / AX-15 Transmission Failure
The Problem
The AX-5 (4-cyl) and AX-15 (6-cyl) manual transmissions wear out around 100–150k miles. 5th gear pops out, synchronizers grind, and seals leak on high-mileage units.
The Fix
Replace transmission fluid with proper MT-90 gear oil first—cheap fluid causes early failure. For worn transmissions, rebuild kits are available or swap to a rebuilt unit. Many owners upgrade to the NSG370 6-speed swap.
DIY
$400–$900
Shop
$1,200–$2,500
06
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Crankshaft Position Sensor Failure
The Problem
A very common issue on early TJs—the crankshaft position sensor (CPS) fails, usually when the engine is hot. The Jeep will stall and not restart until it cools down. Often misdiagnosed as a fuel pump issue.
The Fix
Replace the CPS (located near the bell housing on the 4.0L). It's a 30-minute DIY job. Use an OEM Mopar or Chrysler part for best reliability—aftermarket sensors are known to fail prematurely. Costs $20–$50 in parts.
DIY
$30–$60
Shop
$100–$200
07
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Exhaust Manifold Cracks & Leaks
The Problem
The cast iron exhaust manifold on the 4.0L I6 cracks with age due to heat cycling. Symptoms include a ticking noise on cold startup, smell of exhaust inside the cab, and power loss.
The Fix
Replace the cracked manifold with an OEM unit or upgrade to an aftermarket header (BBK, Edelbrock) for better flow. The header bolts (especially the rear three) often seize—apply penetrating oil days in advance. Budget for broken bolt extraction.
DIY
$80–$200
Shop
$250–$500
08
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Leaking Cylinder Head / Head Gasket
The Problem
High-mileage 4.0L engines develop head gasket failures, often from overheating due to a failed radiator or thermostat. White smoke from exhaust, coolant in oil (milky cap), or rough idle are telltale signs.
The Fix
Head gasket replacement with a new head bolt set. Have the head resurfaced and pressure-tested. While apart, replace the thermostat and water pump. Use an MLS (multi-layer steel) head gasket for better durability over the OEM composite type.
DIY
$200–$450
Shop
$800–$1,800
09
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Leaky Doors & Water Intrusion
The Problem
The half-door seals crack and shrink with age, letting water pour in during rain. Full door versions also develop worn weatherstripping. Water pools on the floor, causing carpet mold and rust.
The Fix
Replace door seals with new foam or rubber weatherstripping. Use Loctite weatherstrip adhesive to bond properly. Drill drain holes in the floor pan to allow water to escape, and replace carpet with marine-grade or all-weather mats.
DIY
$20–$80
Shop
$100–$200
10
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Vacuum Line Deterioration (HVAC / Engine)
The Problem
Rubber vacuum lines crack and collapse with age, causing rough idle, vacuum leaks, HVAC airflow issues (stuck on defrost), and 4WD engagement problems. A very common complaint on 1997–1999 TJs.
The Fix
Inspect all vacuum lines for cracking or brittleness—use an unlit propane torch near lines while idling to find leaks (idle will smooth when propane enters a leak). Replace all rubber lines with silicone vacuum line kits available for ~$30. Takes 1–2 hours DIY.
DIY
$30–$60
Shop
$100–$250
11
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Windshield Cowl & Windshield Seal Leaks
The Problem
The plastic cowl below the windshield traps debris and the rubber windshield seal shrinks and cracks, allowing water to drip onto passengers' feet. Often blamed on the soft top until the real source is found.
The Fix
Remove and thoroughly clean the cowl drain. Replace the windshield seal (the rubber gasket around the glass) using a windshield seal kit. Apply a bead of black silicone to seal any gaps at the corners. Takes about 1 hour DIY.
DIY
$20–$50
Shop
$80–$150
12
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Oil Pressure Sending Unit Failure
The Problem
The oil pressure sending unit on the 4.0L is notorious for failing, causing the oil pressure gauge to read zero or fluctuate wildly. Often mistaken for an actual oil pressure problem—which is actually rare on the 4.0L.
The Fix
Replace the sending unit (located on the front of the engine block, near the oil filter). It's a 15-minute job and costs under $20. Always verify with a mechanical gauge first to confirm there's no actual oil pressure problem before condemning the engine.
DIY
$15–$25
Shop
$80–$120
13
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Worn Front Axle U-Joints & Dana 30 Issues
The Problem
The Dana 30 front axle U-joints and Spicer-style knuckles wear out, especially on lifted or off-road vehicles. A clunking noise on turns or engagement of 4WD indicates worn U-joints or ball joints.
The Fix
Replace front axle U-joints with Spicer or Moog units. Check upper and lower ball joints at the same time. For off-road use, consider installing greaseable U-joints (Spicer 5-760X with grease fitting modification) or upgrading to a Dana 44 axle swap for bigger tires.
DIY
$80–$180
Shop
$200–$400
14
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A/C Evaporator & Heater Core Failure
The Problem
The original heater core and A/C evaporator fail on high-mileage units. Signs include sweet antifreeze smell in the cab, foggy windshield, wet passenger floor, or A/C that blows only warm air.
The Fix
The heater core requires significant dash disassembly—plan a full weekend. The A/C evaporator is in the same box. Replace both at the same time to avoid doing the job twice. Use a quality replacement (ACDelco or OEM Chrysler) and flush the heater hoses before reconnecting.
DIY
$80–$200
Shop
$500–$900
15
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Body Mount Deterioration
The Problem
The rubber body mounts compress and deteriorate over time, causing body-to-frame movement, creaking noises, and misaligned doors. Combined with frame rust, collapsed mounts are extremely common on 1997–2002 TJs.
The Fix
Replace all 8 body mounts with a complete body mount kit. Polyurethane mounts (Energy Suspension, Rough Country) last longer than rubber OEM units. This is often done during a body lift if desired. Treat any rust on the mount towers before reinstalling.
DIY
$60–$150
Shop
$200–$400
16
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Death Wobble (Persistent in Late TJs)
The Problem
Still prevalent on 2003–2006 TJs. By this age, track bars, control arm bushings, and tie rod ends are all worn simultaneously, compounding death wobble. Common above 60 mph after hitting a bump or expansion joint.
The Fix
Complete front-end rebuild: replace track bar with a heavy-duty aftermarket unit (Rubicon Express, TeraFlex), add a steering stabilizer, replace all tie rod ends, ball joints, and control arm bushings. A full rebuild kit from JKS or TeraFlex is the most cost-effective approach.
DIY
$200–$500
Shop
$500–$1,200
17
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NSG370 6-Speed Transmission Issues
The Problem
The NSG370 6-speed introduced in 2005 has notchy shifting when cold, difficulty engaging 3rd and 5th gear, and premature synchronizer wear. Also has a known weak input shaft that can fail under high torque or aggressive off-road use.
The Fix
First, replace factory transmission fluid with Mopar NSG370 specific fluid or Redline MT-90. Cold shifting issues often disappear with proper fluid. For worn synchros, a rebuild kit is available. Avoid hard shifting when cold—allow the fluid to warm up first.
DIY
$30–$500
Shop
$500–$2,000
18
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Throttle Position Sensor (TPS) Failure
The Problem
The TPS on 2003–2006 TJs fails frequently, causing hesitation, surging idle, rough acceleration, and sometimes a no-start condition. A check engine light with codes P0121–P0123 points directly to TPS failure.
The Fix
Replace the TPS (located on the throttle body, two screws). Use OEM Mopar or Bosch for reliability. The sensor must be calibrated after installation—the idle will need to be reset by disconnecting the battery or using a scan tool to clear adaptations.
DIY
$25–$50
Shop
$80–$200
19
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Rear Axle Seal & Dana 44 Leaks (Rubicon)
The Problem
The 2003–2006 TJ Rubicon's Dana 44 front and rear axle seals and pinion seals develop leaks over time. The standard Dana 35 rear axle is also known to leak. Gear oil on the ground or wet drums indicate a seal leak.
The Fix
Replace axle shaft seals and, if leaking, the pinion seal. Check the bearings at the same time—a bad bearing causes excessive shaft movement that destroys new seals quickly. Use National brand seals for good longevity. Change gear oil to Mobil 1 75W-90 LS (if equipped with limited slip).
DIY
$40–$100
Shop
$150–$350
20
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Rusting Frame Rails (Continued Problem)
The Problem
Though later models used slightly improved coatings, 2003–2006 TJs from northeastern/salt-belt states still suffer severe frame rust at the rear frame rails, spring perch areas, and crossmembers by 150k miles.
The Fix
Treat early rust with POR-15 or Chassis Saver. For structural rust, section replacement or full frame replacement is needed. If buying a 2003–2006 TJ, always do a frame inspection from below. Rust proofing (Fluid Film, Woolwax) annually is the best prevention.
DIY
$50–$500
Shop
$600–$2,000+
21
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Power Steering Pump Failure & Leaks
The Problem
Power steering pump seals leak and pumps fail on high-mileage TJs. Symptoms include whining noise while turning, stiff steering, foamy PS fluid, or a visible leak under the pump. More common on TJs with larger tires or a lift.
The Fix
Replace the pump with a rebuilt or new unit. Many owners upgrade to a high-volume/high-pressure pump (Saginaw conversion or aftermarket Borgeson unit) for improved feedback and reliability. Also replace the high-pressure PS line, which commonly leaks at the crimped fitting.
DIY
$80–$180
Shop
$200–$450
22
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Crankshaft Position Sensor Failure (Repeated)
The Problem
Still the #1 no-start complaint on 2003–2006 TJs. The CPS fails after heat soak, causing stalling at operating temperature. Owners stranded at gas stations or in parking lots after hot stops is a signature scenario.
The Fix
Replace CPS with OEM Mopar part only (part #56027997AB or equivalent). The sensor is accessible from below the truck, two bolts. Carry a spare in the glove box—it's a 15-minute roadside repair. A heat shield wrap on the sensor helps extend longevity.
DIY
$30–$55
Shop
$100–$200
23
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Steering Box Wear & Play
The Problem
The recirculating ball steering box wears with age, leading to excessive steering wheel play (1.5–2 inches free movement at the rim), wander on the highway, and difficulty holding a straight line. Worsened by larger tires.
The Fix
First, try adjusting the steering box preload (1 adjusting screw on top of the box)—this often recovers 80% of the play. If worn beyond adjustment, replace with a rebuilt box or upgrade to a Borgeson power steering conversion with a newer Saginaw box for dramatically improved feel.
DIY
$0–$200
Shop
$300–$800
24
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Fuel Injector Clogs & O-Ring Leaks
The Problem
The 4.0L fuel injector O-rings dry out and crack, causing fuel leaks and the smell of raw fuel under the hood. Injectors also clog on high-mileage engines, causing rough idle, misfires, and poor fuel economy.
The Fix
Replace O-rings with a complete injector O-ring kit (~$15). If injectors are clogged, use a fuel injector cleaner or have them professionally ultrasonic-cleaned. For high-mileage engines, a full set of remanufactured injectors (Delphi or RC Engineering) restores performance for about $150.
DIY
$15–$200
Shop
$200–$500
25
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Worn Transfer Case NV231 / NV242 Linkage
The Problem
The transfer case shift linkage on NV231 and NV242 (Rubicon) units wears out, making it difficult to engage or disengage 4WD modes. Worn bushings in the linkage cause a sloppy or vague shift feel, and the transfer case may jump out of 4-Lo under load.
The Fix
Replace the linkage bushings with a polyurethane bushing kit (Poly Performance or Rubicon Express). Also change the transfer case fluid—use ATF+4 for the NV231 and specific fluid for the NV242. Fluid changes alone often fix slipping issues. Check the output shaft seal for leaks.
DIY
$30–$100
Shop
$150–$500
26
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Evaporative Emission (EVAP) System Codes
The Problem
Check engine lights from P0440–P0457 (EVAP system) are extremely common on 2003–2006 TJs. Usually caused by a cracked charcoal canister, leaking EVAP hoses, or a faulty purge solenoid—not dangerous but will fail emissions testing.
The Fix
Start with the cheapest fix first: the gas cap. A loose or cracked gas cap causes 40% of EVAP codes—replace for $10 and clear the code. If it returns, inspect the charcoal canister and purge solenoid. The canister sits near the fuel tank and can be replaced for about $60 DIY.
DIY
$10–$80
Shop
$80–$300
27
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Rear Main Seal Oil Leak
The Problem
The rear main seal on high-mileage 4.0L engines weeps or leaks oil, leaving a puddle under the flywheel/transmission area. On TJs this is a significant job because transmission removal is required for access.
The Fix
Requires transmission removal to access the seal. Replace the one-piece rear main seal with a new OEM or Mahle seal. If the crankshaft seal surface is scored, a speedy-sleeve repair sleeve can be installed without replacing the crankshaft. Replace the clutch while everything is apart to save on labor later.
DIY
$50–$200
Shop
$500–$900
28
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Clutch Master / Slave Cylinder Failure
The Problem
The hydraulic clutch system on 2000–2006 TJs uses a master cylinder and external slave cylinder that wear out. Symptoms include a spongy clutch pedal, difficulty disengaging the clutch, or slow clutch engagement after sitting overnight.
The Fix
Replace both the master and slave cylinders together as a kit—they wear at similar rates and the slave is accessible without removing the transmission. Bleed the hydraulic line thoroughly. Use DOT 3 brake fluid. The whole job takes about 2–3 hours and is very doable DIY.
DIY
$60–$120
Shop
$200–$400
29
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Oxygen Sensor Failure (Upstream / Downstream)
The Problem
O2 sensors on 2003–2006 TJs fail around 100–130k miles, triggering P0131–P0161 codes. Symptoms include poor fuel economy (down 3–5 mpg), rough idle, and failed emissions. The downstream sensor (after the cat) is most commonly guilty.
The Fix
Replace the faulty O2 sensor with a Bosch or Denso unit. An O2 sensor socket (3/8" drive with a notch for the wire) makes the job much easier. Soak the sensor bung with PB Blaster for 24 hours before removal to prevent breaking it off in the exhaust bung. Takes about 30 minutes per sensor.
DIY
$30–$80
Shop
$100–$250
30
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Worn Control Arm & Sway Bar Bushings
The Problem
All four control arm bushings and the front sway bar end link bushings wear out on 2003–2006 TJs, causing clunking over bumps, vague handling, and contributing to death wobble. Rubber bushings compress and crack; typically gone by 120k miles.
The Fix
Replace all control arm bushings with polyurethane units from Energy Suspension or Moog. Note: poly bushings require grease at installation and periodic re-greasing, but last 3–4x longer than rubber. Also replace sway bar end links and bushings at the same time. Full kit costs around $80–$120 in parts.
DIY
$60–$150
Shop
$200–$350