What is the reason for an AT transmission not moving when shifted to D gear?

[BrooklynRose]

AT transmission not moving when shifted to D gear can be due to insufficient transmission fluid or issues with the shift valve. Insufficient transmission fluid: If the automatic transmission fluid is slightly low, it can cause the transmission to jerk when shifting. In severe cases, it may even burn out the transmission. Generally, the automatic transmission fluid (ATF) in a car's automatic transmission should be replaced every two years or every 40,000 kilometers. However, this varies depending on the vehicle model. For Japanese models, it is recommended to replace the fluid every 40,000 to 80,000 kilometers. Vehicles that frequently drive at high speeds should consider replacing the fluid around every 40,000 kilometers. Issues with the shift valve: If there is a noticeable jerk when the automatic transmission shifts gears while driving, or if there is severe vibration when shifting from Park or Neutral to Reverse or Drive during startup, the shift valve may need to be replaced promptly.