D4 in automatic transmission means automatic switching between gears 1 to 4. Types of transmissions: There are mainly two types of automatic transmissions used in vehicles. One is the stepped automatic transmission, and the other is the continuously variable transmission (CVT). The most commonly used in passenger cars is the mechanical CVT, which utilizes a V-shaped metal belt or chain to transmit torque between the driving and driven pulleys in their V-shaped grooves. This type of transmission is typically used in smaller vehicles. Common transmission gear positions: P (Park): When parking the car, the gear selector must be moved to the P position. R (Reverse): Engage this gear when reversing. N (Neutral): The N position is equivalent to neutral and can be used when starting the engine or during towing. D (Drive): For normal driving, place the gear selector in the D position, and the car will automatically shift between gears 1 to 3, 4, or 5. D is the most commonly used gear position. 3 (Third Gear): Also a forward gear, in this position, the transmission automatically switches between gears 1 to 3 without shifting up to 4 or 5. 2 (Second Gear): This position uses either gear 1 or 2, suitable for starting on slippery roads or as a limiting gear for slow forward movement. 1 (First Gear): In this position, the transmission stays in first gear. Some cars also have S (Sport) or L (Low) gear positions.
