Should an automatic transmission be started in P gear or N gear?
3 Answers
An automatic transmission can be started in either P gear or N gear. Some vehicle models, for safety reasons, can only be started in P gear, as starting in N gear may lead to phenomena such as vehicle rollaway. When in N gear, the vehicle's handbrake is not locked, which can result in rollaway and potential traffic accidents. In contrast, P gear does not have the issue of rollaway, as the vehicle is in its safest state. Additionally, starting in P gear can prevent jerking in the vehicle and provides a buffer effect for the transmission when connecting to the engine's output end. It also helps avoid incorrect gear shifts during driving. There is no difference between starting in P gear or N gear, as the structural principles of P gear and N gear are essentially the same. The only difference is that P gear has an additional pawl gear mechanism compared to N gear. Both P gear and N gear disconnect the input shaft and output shaft of the transmission, preventing the output shaft from rotating. The only distinction is that in P gear, the pawl gear mechanism at the end of the output shaft is also locked.
I've been driving automatic transmission cars for over a decade and always start in P gear. This habit has never caused any issues. Starting in P gear is actually the safest because it locks the transmission, preventing any vehicle movement—especially reassuring on slopes. I once tried starting in N gear and nearly rolled backward into another car on my neighborhood slope, which gave me quite a scare. Nowadays, newer cars are smarter, and many won't even start unless they're in P gear. As a pro tip after starting: before shifting to D gear while holding the brake, make sure all warning lights on the dashboard are off before moving. This practice is also good for the engine. Developing good habits can extend your transmission's lifespan—after all, replacing a transmission costs way more than taxi fares.
As a mechanic who often helps friends check cars, I really don't recommend starting the car in N gear. When the transmission is in N gear, it's completely unlocked, and even a slight slope can cause the car to slide, leading to accidents. Manufacturers design the P gear starting circuit to be the safest, so even if you accidentally press the accelerator, the car won't lurch. Just last week, a customer ignored my advice and started the car in N gear, ending up scratching someone's BMW in the parking lot. If you notice a delay when starting, it's best to immediately check the gear position switch or brake switch instead of forcing the key. Also, remember to change the transmission fluid regularly—that's much more practical than worrying about which gear to start in.
