Toyota Sienna transmission failure at various mileage points, significant reliability concerns on Toyota Sienna

Some Toyota Sienna owners report experiencing significant transmission issues, including rough shifting, slipping gears, and complete breakdowns. The 2005 model is particularly noted for frequent transmission failures that can be both costly to repair and pose safety risks. Additionally, owners of the 2017-2018 Sienna have encountered software problems that affect both the engine and transmission, compromising overall performance and reliability. The 2011-2020 models with the 8-speed UA80E automatic transmission have also reported harsh shifting, reduced power, and check engine lights due to incorrectly installed washer tabs. Even the 2021 Sienna has faced reliability concerns, including hybrid system failures and transmission problems such as rough shifting and hesitation, along with stiff suspension leading to a rougher ride. To mitigate these issues, proactive maintenance and early intervention for transmission problems are essential for ensuring the longevity and reliability of the Toyota Sienna.