It's important to note that reliability can vary based on individual experiences, and opinions on which Toyota car is the least reliable can differ. However, based on consumer reports, expert reviews, and historical data, the Toyota Yaris has been considered a less reliable model than other Toyota vehicles. Here are some points to consider:

Transmission Issues: Some owners have reported problems with the automatic transmission in the Yaris, including rough shifting, slipping gears, and premature failure. These issues can be costly to repair and can significantly impact the vehicle's reliability.

Electrical Problems: There have been complaints about various electrical components malfunctioning in the Yaris, such as faulty power windows, malfunctioning dashboard lights, and issues with the audio system. These electrical issues can be frustrating for owners and may require frequent visits to the dealership for repairs.

Build Quality: While Toyota is known for its solid build quality, the Yaris has been criticized for its cheaper materials and less refined interior than other models in the Toyota lineup. Some owners have reported premature wear and tear on interior components, indicating potential durability issues over time.

Engine Reliability: While the Yaris typically comes with reliable engine options, there have been some reports of engine problems, including oil leaks, overheating, and premature engine failure. While these issues may not be widespread, they can still contribute to concerns about the vehicle's overall reliability.

Safety Recalls: Like any mass-produced vehicle, the Toyota Yaris has been subject to safety recalls for various issues over the years. While recalls don't necessarily indicate poor reliability, they can inconvenience owners and raise questions about the vehicle's overall quality control.

It's worth mentioning that newer models of the Yaris may have addressed some of these reliability concerns, and individual experiences can vary widely. However, based on historical data and owner feedback, the Toyota Yaris has been considered one of the less reliable options in the Toyota lineup.