Early automatic transmission vehicles and some cheap units using simple gearboxes still want to give you a way to hold specific gears for as long as you want. Some manufacturers shift from the traditional PRND shift sequence to add other features on their gear selector to achieve this on a budget.
The additions vary depending on the manufacturer. D3 is available in transmissions with a manual mode that lets you select:
- L (low gear)
- 2
- D-3
What Does the D-3 Option Mean on My Transmission Selector?
D3 stands for Drive 3. It’s is the third forward gear in your transmission. Slipping the selector into this position overrides automatic gear changes and holds the transmission in third gear until you take it back to D or shift lower to 2.
While this might seem counterproductive as it negates the essence of an automatic gearbox, it can come in handy during daily driving – as long as you know when to use it.
When to Use D3 in Automatic Vehicles
Knowing when to use fixed gears in your transmission will get you as close to manual transmission as possible without throwing in a good old clutch to your footwell. Since this will override the transmission control in most vehicles, you must first understand the shifting logic in manual transmission:
Shifting at the Right RPM
You have to shift without redlining your engine like a manual transmission case. Redlining happens when your engine revs too hard such that the revolutions per second timer (tachometer) on the dashboard goes into the red zone.
You will hear your engine change pitch and make a lot of noise and sometimes vibrations if you are revving too hard.
To avoid this, you should target shifting into or out of D3 when the revs are right.
- If you are shifting up from D2, execute the shift when the revs build up to a reasonably comfortable level that’s a couple of hundreds from the red zone
- Shift up from D3 to D once the revs build up, and the car can no longer gain or maintain speed without redlining
Pay attention to how the transmission shifts on auto before trying to use D3. This will give you an idea of the RPM sweet spot the manufacturer chose to keep the car. You will also learn how the engine sounds when in this RPM band.
Try to simulate this as much as possible when manually shifting through the D1, D2, and D3 gears.
Matching Your Gear Selection With Driving Speed
When shifting from D to D3, you have to ensure that your vehicle is at an appropriate speed that puts the driveshaft at a reasonable speed compared to engine RPM.
This ensures that the impact of shifting into D3 will not cause instant and hard engine braking since the wheels were spinning way faster than the engine for the D3 drive ratio. If this happens, your car will reduce speed abruptly and rev up hard as the engine is forcefully spun up to speed.
These sudden speed changes put too much strain on your gearbox, the torque converter, and the engine in general. They can also be dangerous to other road users.
There is no rule on how fast you should be before shifting down to D3. You can experiment by inverting the process to find out the sweet spot for your vehicle.
- Start driving from a standstill using L or D1
- Work your way up the gears shifting at the right RPMs
- Note the speed at which you comfortably shift from D3 into drive
- This could be an ideal speed to safely shift back to D3. I’d recommend shaving off some 5 MPH from the reading to be safe.
In most vehicles, anywhere between 25 and 40 miles per hour seems like a good spot to shift down into D3 when necessary. (Don’t take this as the gospel, find the sweet spot for your vehicle)
With that out of the way, we can look at some times when shifting down to D3 would be a good driver decision.
When You Want to Drop a Gear and Accelerate Fast
If your gearbox downshifts slowly when you put the pedal to the metal, you can choose to shift down to D3 manually for the extra punch when passing.
It would work wonders if you are overtaking a slow-moving vehicle on an uphill or even on level ground if the vehicle is moving at speeds slower than 30 MPH.
The lower gear sends more torque to your wheels, making the vehicle accelerate faster. Remember to shift back to D once the engine picks up the slack and revs go up.
Warning: Don’t do this when driving at highway speeds. Third gear might be too low to maintain the speed, especially if you drive a five or six-speed automatic. It would be fine if your vehicle had a four-speed gearbox.
When Driving Down Long Hills
Selecting lower gears when driving downhill and lifting off the accelerator gives you considerable engine braking.
This means you can keep your vehicle rolling at a considerable speed without riding the brakes all the way. Your brakes will remain cool and efficient all the way.
You will not experience any brake fading, and you will retain the ability to stop fast if need be. This is a very useful hack if you live in a hilly area and have to drive down long grades frequently.
Better Throttle Response
Since you have control over what gear your transmission is at any time, you will have better control over how much torque you put to the wheels. This, coupled with the control gearing, gives you an overall better throttle response over engine revving.
Your driving dynamics will change, and you can turn a tame commuter into a somewhat interesting vehicle that’s more engaging to drive.
Can Driving in D3 Damage Your Car?
Driving in D3 will not damage your car if you use it under the right conditions. Using it to engine brake or drop a gear for better acceleration is fine as long as you are at the right speed. However, you could ruin your engine and transmission if you use D3 to redline your vehicle regardless of whether it is intentional or accidental.
Check this too: What Does the O/D Off Light Mean on My Car?
Does D3 Make You Accelerate Faster?
Driving in D3 will not make your vehicle accelerate faster unless you are in the right speed and RPM band.
If you are somewhere between 30 and 35 MPH and your vehicle is in a higher gear, you will feel slightly better acceleration by dropping to D3 and flooring it. The same won’t happen if:
- You were going slower: Third gear might be too high for your engine
- You were going faster already: Third gear will be too high for your engine
ProTip: Since holding D3 could lead to higher engine RPMs by limiting the gearbox from selecting higher gears, it could have the effect of higher fuel consumption – especially if you are in D3 and flooring it.
Bottom Line
D3 is a great way to take some charge of your automatic gearbox and force it to do what you deem best for a given scenario. However, you have to master the art and know what speed and RPM you can shift into and out of D3 to get the best out of your drivetrain.