What Does Park (P) Mean?

Park (P): This gear selection mechanically locks the output shaft of the transmission, restricting the car or truck from moving in any direction. A parking pawl prevents the automatic transmission from rotating, and therefore the car or truck from moving, although the vehicle's non-driven road wheels may still rotate freely. For this reason, it is recommended to use the hand brake or parking brake because this actually locks the rear wheels and prevents them from moving in most cases. This also increases the life of the automatic transmission and the park pin mechanism, because parking on an incline with the automatic transmission in park without the parking brake engaged will cause undue stress on the parking pin. An efficiently-adjusted hand brake should also prevent the car or truck from moving if a worn transmission gear selector accidentally drops into reverse gear during early morning fast idle engine warm ups. It should be noted that locking the automatic transmission output shaft does not positively lock the driving wheels. If one driving wheel slips while the automatic transmission is in "park," the other will roll freely as the slipping wheel rotates in the opposite direction. Only a properly adjusted parking brake can be relied upon to positively lock both of the parking-braked wheels.

It is typical of front-wheel-drive cars for the parking brake to be on the rear non-driving wheels, so use of both the parking brake and the transmission park lock provides the greatest security against unintended movement on slopes. Unfortunately, the rear of most front wheel drive automobiles has only about half the weight on the rear wheel as is on the front wheels, greatly reducing the security provided by the parking brake as compared to either rear wheel drive vehicles with parking brake on the rear wheels which generally have near half of the total vehicle weight on the rear wheels, except for empty pickup and open bed trucks or to front wheel drive vehicles with the parking brake on the front wheels, which generally have about two thirds of the vehicle's weight unloaded on the front wheels.

A car or truck should be allowed to come to a complete stop before setting the automatic transmission into park to prevent auto trans damage. Usually, Park (P) is one of only two transmission gear selections in which the car or truck engine can be started, the other being Neutral (N). In many modern cars and trucks, the driver must have the foot brake applied before the automatic transmission can be taken out of park. The Park position is omitted on buses / coaches with automatic transmission on which a parking pawl is not practical, which must be placed in neutral with the parking brakes set.

Most car and trucks require P or N to be set on the selector lever before the internal combustion engine can be started. This is typically achieved via a normally open 'inhibitor' switch, which is wired in series with the starter motor engagement circuit, and is only closed when P or N is selected, thus completing the circuit when the key is turned to the start position.