If you’ve ever driven a modern vehicle with an automatic transmission, you’ve likely seen the acronym PRNDL (PRIN-dle), even if you don’t remember it. These letters appear next to the shifter, and they stand for park, reverse, neutral, drive, and low—in that order. The order is important, as activist Ralph Nader pointed out in his seminal 1965 book, “Unsafe at Any Speed.” Here, we’ll discuss why that is and how automakers have tried to innovate shifter design while still largely adhering to this pattern.
What Does PRNDL Mean?
- The PRNDL Gear Shift
- The Advantages of the PRNDL Sequence in Automatic Cars
- The Evolution of the PRNDL Gear Shift
- Consequences of Poor Shifter Designs
- Common Issues and Troubleshooting With PRNDL
The PRNDL Gear Shift
An automatic transmission’s functions are pretty self-explanatory, but to recap:
Park is the first position of a PRNDL shifter. When selected, a parking pawl (or pin) slots into a notched wheel on the transmission’s output shaft, locking it—and thus the vehicle’s driven wheels—in place.
Reverse selects a gear in the transmission that rotates in the opposite direction from the others. This allows the car to move backward.
Neutral—as you may know from trips through the car wash or from towing—takes a car out of gear but doesn’t lock the wheels, so an external force can pull or push the vehicle freely.
Drive is the primary shifter position for moving forward, allowing the transmission to use all of its forward gears.
Then there’s Low. The L function is one that many drivers may never use. It forces the transmission to hold a low gear, which makes available a lot of torque but limits the vehicle’s speed. Lower gears employ a different gear ratio, which can be useful when you’re driving up a steep incline and need some extra grunt. It’s also helpful if you’re going downhill for a stretch and don’t want to ride the car’s brakes, as letting the car coast in a low gear amplifies engine braking.
The Advantages of the PRNDL Sequence in Automatic Cars
The PRNDL gear sequence has been around since the 1950s, but it didn’t become the standard pattern until Ralph Nader, in his 1965 book 'Unsafe at Any Speed', took General Motors, Studebaker, and Rambler to task for employing the potentially dangerous PNDLR (pen-ID-ler?) arrangement in several products.
Intuitively, placing the reverse gear last seems like a good choice: Pulling the shifter all the way back will make the car go backward. But as Nader argued in his book, this sequence makes it far too easy for drivers to land in low (a forward gear) and mistake it for reverse; when the driver—whose eyes are presumably fixed on what’s behind them—taps the accelerator, the car won’t move in reverse as expected but instead go forward.
Nader pointed out a few instances where this very thing caused an injury- or fatality-inducing crash and advised the government to standardize the shift pattern for reasons of safety. He succeeded, with the federal government mandating, in 1971, that neutral must fall between reverse and drive.
The Evolution of the PRNDL Gear Shift
While automakers are required by law to put neutral between reverse and drive, that hasn’t stopped them from playing around with the other positions. For instance, several years ago, BMW, in an effort to make the dual-clutch automatic transmission in M models feel more like a manual, installed a shifter without a park position. The driver would bring the car to a stop, lift the parking brake, and shut off the car to engage park.
Moreover, in many modern vehicles, you’ll see L replaced with another option, such as M, S, or B. These modes can perform the same function(s) as L, but they differ in subtle ways.
M is a manual mode that allows the driver to select the desired forward gear, just as they would in a manual-transmission vehicle (albeit without the clutch pedal). Typically, the letter appears sandwiched between a plus sign and a minus sign and may require the driver to purposefully move the shifter out of the direct PRND line. Once there, toggling the shifter toward the plus sign will advance the transmission to a higher gear, while moving it toward the minus sign will select a lower gear and accomplish what L does.
S (for sport) mode varies by manufacturer and often affects several aspects of a car’s character, but with regard to the transmission, it should make the gearbox hold lower gears longer than drive would for the sake of performance.
In eco-friendly vehicles, the shifter may have a B setting, which stands for braking. B, like S, also keeps the vehicle in a low gear, but it’s for the engine-braking purpose rather than performance. In the electric Volkswagen ID.4—which doesn’t have an engine but an electric motor—B increases the level of regenerative braking to help the car slow without the use of the friction brakes.
The Tesla Cybertruck doesn’t even have an L or equivalent gear. Its overhead push-button shifter shows just PRND. While this shift pattern is hardly unique to Teslas, the lack of a low setting does seem in keeping with the EV maker’s mission to simplify and automate the driving experience.
Consequences of Poor Shifter Designs
The advent of shift-by-wire technology (that is connecting components by wires instead of mechanical parts) in the 1990s gave automakers more freedom in shifter design and placement, as it meant they could replace a mechanical connection between the shifter and transmission with an electronic one.
While many automakers still employ a traditional automatic transmission shifter position located within the center-console or a steering-column stalk, they may have adjusted how it moves (using a rocking or twisting design rather than a position-sensitive one).
Others have tried to totally reinvent the interface. For instance, the last-gen Toyota Prius has a sort of joystick that juts out of the center stack. The current Ram 1500 has a dial tucked away to the right of the steering wheel. The 10th-generation Honda Accord (with the ten-speed transmission) has push buttons. And the pre-refresh VW ID.4 has a gauge-cluster-mounted knob that you twist clockwise for drive (or braking) and counterclockwise for reverse.
Some designs have been more successful than others, with a few leading to unintentional consequences. Eight years ago, Fiat Chrysler recalled more than 1 million vehicles after its monostable shifter (which returns to a default central position after each selection rather than moving to a discrete position for each step in the PRNDL pattern) caused many drivers to believe the vehicle was in park when it was in fact in neutral. In numerous instances, the driver left the vehicle, which then rolled of its own accord. Crashes ensued. FCA came up with a software fix to mitigate the problem: Whenever the driver opens their door, the vehicle will automatically engage park. But it soon abandoned this shifter design altogether, reverting to a more traditional one.
Other designs are just frustrating. The rotary shifter in certain Genesis vehicles, for example, sits just aft of a similarly sized dial that controls the infotainment system. While mistaking one for the other won’t cause a catastrophic problem, it does lead to driver confusion.
Common Issues and Troubleshooting With PRNDL
It’s not unheard of for a vehicle’s gear selector to indicate the wrong gear. On old models, the mechanical linkage that moves the pointer or highlight over the PRNDL shift pattern may be broken or loose, causing the shifter’s position to no longer line up with the appropriate letter. And not too long ago, Ford had to recall lots of Fusions and Escapes when bad bushing connections caused the shifter cable to break and the indicator to read incorrectly.
In modern cars, an electrical issue is often to blame. Perhaps the PRNDL letter isn’t lighting up when you select that position or the digital instrument cluster isn’t displaying the correct letter. This could be because of a malfunctioning sensor, a poor wire connection, a faulty shift linkage, or a defective transmission control module. You might be able to suss out the issue with an OBD-II code reader that plugs into your car, but fixing it will likely require some disassembly. If that task seems daunting, it’s best to leave the repair to a trained mechanic.
