The 2009 4Runner is mechanically solid, but the 4.0L V6 has a catastrophic piston skirt failure problem around 100k-150k miles, and both engines suffer from secondary air injection system failures. The 4.7L V8 is generally more reliable but drinks fuel.
4.0L V6 Piston Skirt Failure (Widespread Engine Destruction)
Common · high severityTypical onset: 100,000-150,000 mi
Symptoms: Metallic knocking on cold start that disappears when warm, Sudden catastrophic knocking and loss of power, Metal shavings in oil, Check engine light with misfire codes
Fix: Piston skirts crack and disintegrate, aluminum debris circulates and destroys bearings. Requires complete engine rebuild or replacement. 20-30 hours labor for used engine swap, 40+ for rebuild.
Estimated cost: $4,500-8,000
Secondary Air Injection System Failure
Common · medium severityTypical onset: 80,000-120,000 mi
Symptoms: P0410, P0418, P0419 codes, Check engine light on cold starts, Air pump rattling or seized, Smog test failure in states requiring it
Fix: Air pump motor fails or check valves stick. Many owners delete system where legal since it only runs briefly on cold start for emissions. Repair involves pump, valves, and sometimes hoses. 2-4 hours labor.
Estimated cost: $800-1,500
Transmission Oil Cooler Line Corrosion and Leaks
Common · medium severityTypical onset: 90,000-140,000 mi
Symptoms: Transmission fluid dripping from radiator area, Pink fluid puddles under vehicle, Low transmission fluid warning, Burnt transmission smell if run low
Fix: Steel cooler lines rust through where they connect to radiator, especially in salt states. Replace both lines preventively when one fails. 2-3 hours labor plus fluid flush.
Estimated cost: $400-700
Lower Ball Joint Wear
Occasional · high severityTypical onset: 100,000-150,000 mi
Symptoms: Clunking over bumps, Wandering steering, Excessive tire wear on inside edges, Play in wheel when lifted and pushed/pulled
Fix: Lower ball joints wear, especially with lifted vehicles or aggressive offroad use. Failure can cause wheel to separate. Replace both sides with OEM or quality aftermarket. 3-4 hours labor for both sides.
Estimated cost: $600-1,000
Front Driveshaft Center Support Bearing Failure (4WD models)
Occasional · medium severityTypical onset: 90,000-130,000 mi
Symptoms: Vibration at highway speeds, Clunking when engaging 4WD, Squealing from underneath while driving, Vibration worse under acceleration
Fix: Center support bearing on two-piece front driveshaft wears out. Entire driveshaft typically replaced as assembly. 2-3 hours labor.
Estimated cost: $600-900
Exhaust Manifold Cracking (4.0L V6)
Occasional · low severityTypical onset: 120,000-180,000 mi
Symptoms: Ticking noise from engine bay on cold start, Exhaust smell in cabin, Failed emissions test, Visible cracks in manifold castings
Fix: Cast iron manifolds crack between ports from heat cycling. Both sides eventually crack. Aftermarket headers or OEM replacements. 6-8 hours labor for both sides due to access issues.
Estimated cost: $1,200-2,000
Dash and A-Pillar Cracking
Common · low severitySymptoms: Cracks across top of dashboard near windshield, A-pillar trim cracking near airbag cover, Squeaks and rattles from dash area, Visible stress fractures in sunlight
Fix: Poor quality plastic on dash and A-pillar trim cracks from UV exposure and temperature cycling. Cosmetic issue but expensive to fix properly. Dash replacement requires complete removal. 8-12 hours labor for dash.
Estimated cost: $1,500-2,500
Buy the 4.7L V8 if you can afford the fuel; avoid high-mileage 4.0L V6 models unless engine has been replaced or verified knock-free.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.