What is the purpose of the D3 Gear in my Automatic Transmission?

D3 Gear

Modern cars get more and more functions every year.

Some functions are more necessary than others, but each function plays a role if you look closer.

One of these “strange” features is, as many people would say, the D3 transmission in automatic transmissions.

Most of us have never used this gear before and probably will not do so in the future. But what is the purpose of this D3 gear, and in what situations should it be used? In this article, we will go through everything about the D3 transmission: some necessary information, its meaning, and some other general information about automatic transmission. Let’s get started!

D3 Gear Meaning & Purpose

The D3 transmission stands for Drive 3, which means that when you have selected this gear, the gearshift locks the automatic transmission in 3rd gear. 

D3 Gear

“But I have an automatic transmission and no manual transmission with gears!” You might think. Well, even if your transmission is automatic, you have gears in it. The only difference is that there is a control unit with a hydraulic pump and some valves that shift for you instead of doing it yourself.

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What’s the purpose of the D3 gear then?

Well, there are many different situations where you should use the D3 gear. If you live in a colder country with snow and ice, you are probably more familiar with this equipment than if you live in a warmer state.

If you’re driving up a slippery and steep hill, you may want to disable the ABS/ESP system and select the D3 gear to make sure the transmission doesn’t change gear while the tires are spinning, causing a drop in speed and leaving you stuck in mud or snow.

D3 Gear Mud Snow

Another common situation is when you are driving down a long hill. If you select D3 gear, it locks into third gear. The problem with automatic gearboxes is that they often run at low revs and the engine brake is almost non-existent. This is the advantage of a manual gearbox: you always have direct contact with the drive wheels, and the engine helps you to brake the speed instead of constantly pressing the brake pedal.

However, if you have selected the D3 gear when you are driving downhill, it will bring your engine up to a higher RPM, which will cause more backpressure and engine braking, and it will act more like a manual gearbox. You are thus able to reduce and control your speed with the help of the engine. This saves fuel and a lot of braking when you drive downhill for long distances.

Many truck drivers use this method to lock a lower gear when driving downhill to prevent the brake pads from overheating and save some fuel. In the worst cases, overheated brake pads can cause the brakes to fail and this could lead to a dangerous situation, especially when going downhill, as you might imagine. It also saves you expensive repair costs for replacing your brake discs and brake pads in a garage.

Pros of using the D3 gear

  1. You will reduce mileage when going downhill
  2. You will minimize brake repair costs when going downhill
  3. It will give you more control when your car is stuck or going through bad terrains
  4. It will provide you with more control on slippery surfaces
  5. It will be easier to handle if you are towing another vehicle behind you

What about the other D1, D2, D4 gear on my transmission?

The same applies to these gears, and the only difference is the speed of the transmission. The number behind it tells you which gear should be locked. The letter L stands for Low, which is in most cases a lower gear than the first gear.

So which gear is the best gear?

This depends on the situation, and you need to use common sense when making your choice to ensure that your engine does not rev too high or too low. It also depends on what gear ratio your gearbox and axle have, so it is impossible to give an exact answer for all car models.

However, if you get stuck in the snow, you will probably want to choose the lowest or second gear to prevent the wheels from spinning too fast. This will only cause the wheels to spin down into the snow and you will be stuck even more than before.

If you are driving uphill on a slippery surface, you may want to select gear D3 or D4. If you want to use it as an engine brake, you will have to try out for yourself whether 2nd, 3rd, or 4th gear gives the best engine brake without too high a speed. A recommended RPM is about 3,000 RPM downhill, and you can even go higher if the hill is exceptionally steep.


As you get deeper into the subject, the D3 transmission is perfect for many different situations, if you know when to use it. This information can save you a lot of money by avoiding the need to replace brake pads and discs, especially if you live in an area with bad terrain or steep hills. It can also save you if you ever get stuck with your car in mud or snow.

I hope you have learned some things from this article and feel comfortable using this equipment to your advantage. If you have any further questions about this topic that you would like to have answered, please comment below and I will answer all your questions as soon as possible. If you have any further questions, you can view our other posts by using the search function on our website.

Written by: Magnus Sellén

Founder, owner & main author of Mechanic Base. I have been repairing cars for more than 10 years, specialized in advanced diagnostics & troubleshooting. I have also been a drifting driver and mechanic for over 7 years.