The Toyota 3MZ-FE is the 3.3L V6 found in the 2004-2010 Sienna, Camry V6, Highlander, Solara, Lexus RX330, and ES330. Solid, understressed engine with two well-known issues.
Reliable platform overall. Knock sensor wiring harness corrosion is the famous fault. Sludge from skipped oil changes is the other.
Wires under the intake manifold corrode and short. Throws P0325/P0330. Cheap part, expensive labor because the intake has to come off. Updated harness is mandatory at this age.
View diagnosis →Like the 2AZ-FE, the 3MZ will sludge if oil changes are skipped or wrong oil is used. Not a class action like the 2AZ but documented. Verify maintenance records.
View diagnosis →Rubber section of the VVT-i oil line can rupture, dumping oil on the exhaust manifold (fire risk). Toyota issued an updated all-metal line.
View diagnosis →PS pump bearings get noisy around 120K. Replacement is straightforward.
View diagnosis →Interference engine. Belt + water pump + tensioner is mandatory at 90,000 miles.
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2004-2005 (highest sludge complaint rate, early VVT-i line failures)
2007-2010 Highlander/Sienna (updated oil line, harnesses still old)
Annual maintenance $400-600. Timing belt service $700-1,100. Knock sensor harness $500-1,200. Total non-routine over 200K: $3,500-5,500.
If your Toyota is throwing a check engine light, these are the codes most often associated with the problems above. Click any code for full diagnosis steps and typical repair costs.
🔬 Run a free AI diagnosis →Yes - mechanically solid. The knock sensor harness is the classic failure point and is cheap to fix once you commit to the labor.
Easily 250,000 miles with routine oil changes and timing belts done on time.
Yes - timing belt with 90,000-mile replacement interval. Interference engine.
Almost always the knock sensor wiring harness corroding under the intake. Replace the harness, not just the sensor.
No - the 2AZ-FE was the focus of the class action. The 3MZ can sludge from neglect but was not part of the settlement.