While the majority of car enthusiasts know exactly what the PRNDL letters mean on automatic transmission’s shifter, many drivers may may wonder what PRNDL means. Surprisingly, the acronym holds more meaning than most people realize. Shift position/selection is critical to the operation and diagnosis of an automatic transmission. In this article, we’ll cover the PRNDL meaning, the information behind each letter, alternative patterns, and their effects on the transmission.
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What Is An Automatic Transmission?
An automatic transmission is one that shifts gears automatically. Instead of a clutch, the conventional automatic transmission uses a torque converter. All the shifting is done automatically through the use of hydraulics, which is why the condition of automatic transmission fluid is so important. The gears are indicated by the letters ‘PRNDL’ on most vehicles, and all shifting is done by the transmission itself.
Auto transmission cutaway. (Source: MotoVisuals)
Types Of Automatic Gear Shifts / Selectors
There are essentially three types of gear shifters you may find on vehicles equipped with automatic transmissions. These shifters control the positioning of the ‘manual valve’. The manual valve is located inside the valve body of the automatic transmission. Transmission shifter cables can stretch and wear over time, usually needing to be adjusted at some point.
Automatic transmission shifter. (Source: MotoVisuals)
Column Shifter
Column shifters are becoming less common in automatic transmissions. They use a cable connected to the transmission. The gear selector is located near the steering wheel or steering column.
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Floor / Console Shifter
This is the most common type of gear selector found on automatic transmissions. This selector is found on the floor or center console of the vehicle. These also use a shifter cable connected to the transmission.
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Dial-Type Shifter
Dial-type shifters are newer. Mostly electronic, they eliminate the need for a transmission shifter cable. One example of a dial-type shifter can be found in the Chrysler Pacifica minivan.
Chrysler
Shifter Patterns
These are the shift patterns that your vehicle may use:
PRNDL
PRNDS
PRNDM
PRND + / –
PRNDB
PRND321
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P On A Car Shifter
The P sits at the uppermost position. The P stands for Park. When the transmission is in park, the driving clutches of the transmission are not powered and a parking pawl engages the output shaft to prevent rotation.
Always engage the parking brake when parking on hills to prevent wear on the parking pawl.
R On A Car Shifter
The R stands for Reverse. During the reverse gear selection, the transmission applies a holding device to change the rotation of the planetary gear set. This allows the output shaft to rotate in the opposite direction, driving the vehicle backwards.
N On A Car Shifter
The N stands for Neutral. During the neutral selection, the transmission does not power driving clutches and does not engage the parking pawl. Neutral is often used to tow the vehicle or to move the vehicle when it’s unable to move under its power.
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D On A Car Shifter
The D stands for Drive. During the Drive gear selection, the transmission will power various driving clutches and holding devices. This will allow the vehicle to move forward and achieve different gear ratios. Underdrive gears multiply torque to allow the vehicle to tow/haul or climb steep hills. Overdrive gears allow the engine to operate at a lower RPM, improving fuel efficiency.
L On A Car Shifter
The L stands for Low. Typically, the transmission will allow additional holding/driving devices to engage, providing engine braking and limited upshifts. Most transmissions will only allow gears 1-2 to be engaged under the Low selection. On certain cars, there are also numbered positions on the shifter, indicating the maximum gear into which the transmission will upshift. In the four-speed automatic transmission shown in the picture below, for instance, the driver can select numbers 1, 2, or 3, limiting the number of upshifts depending on the driving conditions.
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M / S On A Car Shifter
What does M mean on a car? Lately, modern automatic transmissions may have the M (manual) or S (sport) letter designations on the gear selector. Some use buttons, paddle shifters, or the shifter to control shifts. These selections allow the driver to manually shift the transmissions. Some applications do a better job of this than others. It gives the driver more control, controlling when upshifts or downshifts happen. This works well on the track or when sportier driving is preferred.
Other Gear Selections
There are a few other gear selections, such as B, Sport, and E. These selections will prioritize shift pressures and points to maximize traction, power, or fuel economy. The B is typically used on hybrids. This gear selection focuses on improving braking. Sport, like the S selection, will shift the transmission later, delivering more power. E stands for Eco or Economy and the focus there is to maximize fuel efficiency.
Valvebody animation (MotoVisuals)
Overview: Automatic Transmission Symbols
P
Park
R
Reverse
N
Neutral
D
Drive
L
Low
M
Manual
S
Sport
1, 2, 3, 4 etc.
Limit upshifts to the maximum corresponding gear number
E
Eco/Efficiency
B
Braking
How Shift Position Helps In Diagnosis
The shifter selection controls the positioning of the manual valve inside the valve body, which serves as a hydraulic brain or control unit for the automatic transmission. Automatic transmissions depend on hydraulic circuits to control planetary gear sets. A single planetary gear set can achieve four speeds or ranges: Underdrive, overdrive, direct-drive, and reverse.
The shifter position will alter the driving and holding members that control the gear set. Through this, we can diagnose which clutches are failing inside the transmission. The shifter further affects the transmission by controlling the hydraulic line pressure going to the internal clutches.
Automatic transmission cutaway. (Source: MotoVisuals)