The 2009 Sienna with the 3.3L V6 is generally reliable, but suffers from catastrophic oil consumption and engine sludge issues that can destroy the motor, plus a transmission oil cooler design flaw that's a ticking time bomb for the transmission.
Excessive Oil Consumption / Piston Ring Failure
Common · high severityTypical onset: 80,000-150,000 mi
Symptoms: Burning through 1+ quart of oil every 1,000 miles, Blue smoke from exhaust on cold start or acceleration, Check engine light for misfire codes, Carbon buildup on pistons causing rough idle
Fix: This is the infamous Toyota 3.3L oil consumption defect. Piston rings fail and allow oil past into combustion chambers. Proper fix requires engine teardown, new piston rings, cleaning carbon buildup. If caught late, you're looking at short block replacement. 18-25 labor hours for full internal engine work.
Estimated cost: $3,500-6,500
Transmission Oil Cooler Line Failure
Common · high severityTypical onset: 60,000-120,000 mi
Symptoms: Pink milkshake in coolant reservoir (coolant mixed with ATF), Transmission slipping or harsh shifts, Overheating transmission, Engine overheating in severe cases
Fix: The internal transmission cooler inside the radiator fails, allowing coolant and ATF to mix. Coolant destroys the transmission. Must replace radiator, flush entire cooling system AND transmission, replace transmission if contamination went too far. If caught immediately: radiator + flushes = 4-6 hours. If transmission damaged: add 12-18 hours for rebuild/replacement.
Estimated cost: $800-1,200 (caught early), $3,500-5,500 (transmission damaged)
Engine Sludge Buildup (Oil Maintenance Related)
Occasional · high severityTypical onset: 90,000-140,000 mi
Symptoms: Ticking or knocking from valve train, Low oil pressure warning, Engine runs rough or loses power, Complete engine seizure in worst cases
Fix: The 3.3L is extremely sensitive to oil change intervals. Extended oil changes create sludge that blocks oil passages and starves bearings. If caught early, aggressive engine flush treatments might help (2 hours). If sludge caused bearing damage, you're into head gasket replacement or full engine rebuild territory. 20-30 hours for complete rebuild.
Estimated cost: $200-500 (preventive flush), $4,500-7,500 (rebuild)
Transmission Mounts Deteriorating
Common · medium severityTypical onset: 80,000-130,000 mi
Symptoms: Clunking when shifting from park to drive, Excessive vibration at idle with vehicle in gear, Visible engine/transmission movement when accelerating
Fix: Hydraulic transmission mounts fail and cause harsh shift feel. Front and rear trans mount replacement. 2-3 hours labor depending on which mount(s).
Estimated cost: $300-600
EVAP System Canister and Purge Valve Failure
Occasional · low severityTypical onset: 100,000+ mi
Symptoms: Check engine light with P0440, P0441, P0446 codes, Difficulty fueling (pump clicks off repeatedly), Fuel smell near rear of vehicle
Fix: Charcoal canister saturates or purge valve sticks. Replace canister and/or purge valve. 1.5-2.5 hours depending on component location.
Estimated cost: $400-800
Power Sliding Door Cable and Motor Failure
Occasional · low severityTypical onset: 70,000-120,000 mi
Symptoms: Door opens partially then stops, Grinding or clicking noise from door track, Door won't latch properly, Error messages on dash about door system
Fix: Cables fray or motors wear out on power sliding doors. Cable replacement involves door disassembly and tensioning. Motor replacement is more straightforward. 2-4 hours per door depending on what failed.
Estimated cost: $500-1,200 per door
Buy only with complete service records showing religious oil changes and proof the transmission cooler was replaced preventively or monitored closely—otherwise you're gambling on a $5k-7k engine failure.
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.