When can the P gear of an automatic transmission be used?
4 Answers
Automatic transmission's P gear can be used when parking. The P gear locks the transmission. On very steep slopes, remember to firmly engage the handbrake, otherwise it may cause damage to the transmission locking mechanism. Whether using a gear lever or a rotary knob to switch to P gear, after pushing to P gear triggers the electrical signal, the control unit will engage the pawl into the ratchet wheel. During parking, the pawl and ratchet wheel are only engaged without contact, remaining in a ready state, and the pawl won't be damaged even with prolonged use. If the ratchet wheel actively outputs torque, the consequences could be quite severe. If the vehicle is rear-ended at high speed while parked in P gear, the best possible outcome would be the ratchet wheel pushing against and bouncing off the pawl, or the pawl deforming while the ratchet wheel remains undamaged.
I've been driving a taxi for twenty years, and let me tell you, the P gear is not something to be used carelessly. It's essentially a transmission lock mechanism that should only be engaged when your vehicle comes to a complete stop. For instance, when waiting for friends in an underground mall parking lot, I always shift to P gear and engage the handbrake – this dual protection gives me peace of mind. I've seen rookies use P gear at red lights get rear-ended, resulting in completely wrecked transmissions that cost half an engine's price to repair. For quick stops like picking up packages, I prefer shifting to N gear with the handbrake – it's fast and safe. Remember two golden rules: Never engage P gear while the car is still rolling (you'll hear awful gear grinding noises), and never treat P gear as a parking brake on steep slopes (its locking force simply can't handle it).
When I first got my driver's license, my instructor repeatedly emphasized: P gear = true parking gear. The habit I've developed now is: after the car comes to a complete stop, first press the brake pedal firmly, then pull the handbrake to the top position, and only then shift to P gear and turn off the engine. When queuing to pick up my child from school, just shift to N gear and press the brake—constantly switching to P gear is bad for the locking mechanism. Once, on a slope, I forgot to pull the handbrake and directly pushed to P gear. When I started the car again, the gear shift lever got stuck, and the clunking sound scared me into a cold sweat. Now, if I park on a slope, I first shift to N gear, pull the handbrake tight, wait for the car to completely stabilize, and then shift to P gear. By the way, when using an automatic car wash, always shift to N gear—shifting to P gear will let the conveyor belt drag the car, which is particularly harmful to the transmission.
With ten years of auto repair experience, I've seen too many cases of P gear misuse. Essentially, the P gear is a mechanical lock for the gear. It's most needed in three daily scenarios: long-term parking, locking the car after turning off the engine, and parking on steep slopes. However, it's crucial to note that engaging P gear before the car comes to a complete stop can subject the locking pin to an impact force of up to half a ton when it hits the gear, and repairing the transmission can cost at least three to four thousand. For traffic lights lasting over 90 seconds, I recommend using P gear, but for shorter stops, N gear is more convenient. Once, a car owner complained about severe gear shifting impacts, and upon disassembly, we found the P gear locking teeth completely worn out—it turned out he engaged P gear even while waiting for the elevator, switching it three to four times per minute, leading to cumulative metal fatigue damage.
