Editing Automatic transmission (section)

===Gear selectors===
{{main|Gear stick #Automatic transmission}}
The gear selector is the input by which the driver selects the operating mode of an automatic transmission.<ref>{{cite book|title=Automatic transmissions and transaxles|author=Thomas W Birch|publisher=Pearson Education|place=Upper Saddle River, N.J.|year=2012|isbn=9780132622271}}</ref> Traditionally the gear selector is located between the two front seats or on the steering column, however electronic rotary dials and push-buttons have also been occasionally used since the 1980s, as well as push buttons having been used in the 1950s and 1960s by [[Rambler (automobile)]], [[Edsel]], and most famously, by [[Chrysler]]. A few automobiles employed a lever on the instrument panel, such as the 1955 Chrysler Corporation cars, and notably, the Corvair.

====P–R–N–D–L positions====
Most cars use a "P–R–N–D–L" layout for the gear selector, which consists of the following positions:<ref>{{cite web |url=https://www.ecfr.gov/current/title-49/subtitle-B/chapter-V/part-571/subpart-B/section-571.102 |title=Standard No. 102; Transmission shift position sequence |website=Code of Federal Regulations |at=Title 49 § 571.102 |access-date=August 16, 2023}}</ref>

* '''Park''' (''P''): This position disengages the transmission from the engine (as with the ''neutral'' position), and a [[parking pawl]] mechanically locks the output shaft of the transmission. This prevents the driven wheels from rotating to prevent the vehicle from moving. The use of the [[hand brake]] (''parking brake'') is also recommended when parking on slopes, since this provides greater protection from the vehicle moving. The ''park'' position is omitted on buses/coaches/tractors, which must instead be placed in ''neutral'' with the air-operated parking brakes set. Some early passenger car automatics, such as the pre-1960 [[Chrysler]] cars and the [[Corvair Powerglide]], did not have the ''park'' feature at all. These cars were started in ''neutral'' and required the driver to apply a parking brake when parked. The original [[Hydra-Matic]] from GM instead engaged a parking pawl when placed in ''reverse'' with the engine off, thus dispensing with a ''park'' position until the adoption of the Controlled Coupling Hydra-Matic in 1956.<br>The ''park'' position usually includes a lockout function (such as a button on the side of the gear selector or requiring that the brake pedal be pressed) which prevents the transmission from being accidentally shifted from ''park'' into other gear selector positions. Many cars also prevent the engine from being started when the selector is in any position other than ''park'' or ''neutral'' (often in combination with requiring the brake pedal to be pressed).
* '''Reverse''' (''R''): This position engages ''reverse'' gear, so that the vehicle drives in a backwards direction.<ref>{{cite web|url=https://www.merriam-webster.com/dictionary/reverse%20gear |title=Reverse Gear |publisher=Merriam-webster.com |access-date=2018-06-24}}</ref> It also operates the reversing lights and on some vehicles can activate other functions including [[parking sensor]]s, [[backup camera]]s and reversing beepers (to warn pedestrians).<br>Some modern transmissions have a mechanism that will prevent shifting into the ''reverse'' position when the vehicle is moving forward, often using a switch on the brake pedal or electronic transmission controls that monitor the vehicle speed.
* '''Neutral''' (''N''): This position disengages the transmission from the engine, allowing the vehicle to move regardless of the engine's speed. Prolonged movement of the vehicle in ''neutral'' with the engine off at significant speeds ("coasting") can damage some automatic transmissions, since the lubrication pump is often powered by the input side of the transmission and is therefore not running when the transmission is in ''neutral''. The vehicle may be started in ''neutral'' as well as ''park''.
* '''Drive''' (''D''): This position is the normal mode for driving forwards. It allows the transmission to engage the full range of available forward gear ratios.
*'''Low''' (''L''): This position provides for engine braking on steep hills. It also provides for a lower gear ratio for starting out when heavily loaded.

Some automatic transmissions, especially by [[General Motors]] from 1940 to 1964, used a layout with ''reverse'' as the bottom position (e.g. N–D–L–R or P–N–D–L–R).<ref>{{cite news |url=https://www.thestar.com/autos/2016/11/12/prndl-why-mess-with-it.html |title=PRNDL — why mess with it? |work=Toronto Star |first=Jim |last=Kenzie |date=November 12, 2016 |access-date=August 16, 2023}}</ref>{{failed verification |date=August 2023}}

====Other positions and modes====
[[File:Aero Star MP37F Allison Shift selector and Parking brake lever.jpg|thumb|right|Push-button gear selector in a 2010–2014 [[Mitsubishi Fuso Aero Star]] bus]]
Many transmissions also include positions to restrict the gear selection to the lower gears and engages the [[engine braking|engine brake]]. These positions are often labelled "L" (low gear), "S" (second gear) or the number of the highest gear used in that position (eg 3, 2 or 1). If these positions are engaged at a time when it would result in excessive engine speed, many modern transmissions disregard the selector position and remain in the higher gear.

In descending order of the highest gear available:
* '''3''': Restricts the transmission to the lowest three gear ratios. In a 4-speed automatic transmission, this is often used to prevent the car shifting into the [[overdrive (mechanics)|overdrive]] ratio. In some cars,{{which|date=November 2020}} the position labelled "D" performs this function, while another position labelled "OD" or a boxed "[D]" allows all gears to be used.
* '''2''' (also labelled "S"): Restricts the transmission to the lowest two gear ratios. In some cars, it is also used to accelerate from standstill in 2nd gear instead of 1st, for situations of reduced traction (such as snow or gravel). This function is sometimes called "winter mode", labelled "W".
* '''1''' (also labelled "L"): Restricts the transmission to 1st gear only, also known as a "low gear". This is useful when a large torque is required at the wheels (for example, when accelerating up a steep incline); however use at higher speeds can run the engine at an excessive speed, risking overheating or damage.

Many modern transmissions include modes to adjust the shift logic to prefer either [[Engine power|power]] or [[Fuel economy in automobiles|fuel economy]]. "Sport" (also called "Power" or "Performance") modes cause gear shifts to occur at higher engine speeds, allowing higher acceleration. "Economy" (also called "Eco" or "Comfort") modes cause gear shifts to occur at lower engine speeds to reduce fuel consumption.

====Manual controls====
{{main|Manumatic}}
[[File:Paddle Shifter - 2013 BMW X5 xdrive 35i (9709131265).jpg|thumb|Paddle shifter (labelled "+") in a 2013 [[BMW X5]] ]]
Since the 1990s, systems to manually request a specific gear or an upshift/downshift have become more common. These ''manumatic'' transmissions offer the driver greater control over the gear selection that the traditional modes to restrict the transmission to the lower gears.

Use of the manumatic functions are typically achieved either via paddles located beside the steering column, or "+" and "-" controls on the gear selector. Some cars offer drivers both methods to request a manual gear selection.
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