The GMC Sierra is General Motor’s luxury truck that can still get its hands dirty. With a wide array of engines to choose from, this full-size pickup can fulfill even the highest demands. It also comes with optional 4WD for those who want to traverse challenging terrain in comfort. So, let’s find out how you can engage the Sierra’s four-wheel-drive system.
How to engage 4WD on a Sierra?
You can engage the GMC Sierra 4WD system with a knob that’s easily accessible from the driver’s position. With it, you can choose between Two-High (2), Four-High (4), and Four-Low (4¯). The GMC Sierra allows drivers to shift between Two-High and Four-High without stopping the truck.
But, to engage Four-Low, you must come to a complete stop. Then, you must shift into neutral before you engage the Four-Low. After this, you can slip into gear. Repeat process to go from Four-Low to Four-High.
The terms “High” and “Low” refer to the range in which the gears are. The GMC Sierra 4WD comes with a transfer case that can select between high-range and low-range gearing.
The High-range option has a gear ratio that’s ideal for highway and general driving conditions. In it, the Sierra has lower torque but can reach higher speeds.
On the other hand, the Low-range setting has a higher gear ratio. This increases torque but decreases final speed.
The transfer case allows you to choose between sending power to two or four wheels in the High-range setting. Hence, the terms Two-High, for the rear wheels, or all four wheels (Four-High).
You can only engage low-range gearing on all four wheels, as it’s designed to traverse challenging terrains. The driving conditions are also critical for the safe use of 2WD and 4WD. You should only use 4WD when traction is limited. We’ll discuss what are the requirements for each mode further down in this article.
But, first, let’s talk about what is a 4WD system.
What is a 4WD system?
A 4WD system allows the driver to send power to all four wheels when it’s necessary. Plus, some increase the torque to get out of rugged terrains such as mud, deep water, sand, and snow.
Vehicles that have 4WD also come with a transfer case. Instead of standard transmissions, a transfer case has two sets of gears: high-range and low-range. Pushing a button, twisting a knob, or pulling on a lever, drivers can select between these two modes.
High-range gearing uses standard gear ratios. This means that they deliver the best power and torque for city and highway driving. Usually, they’re are smaller. This means that the difference in size between gears isn’t that drastic.
Low-range gearing uses specialized gear ratios. The difference in size between gears is higher, so a smaller pinion moves a bigger one to generate more torque. This translates to slower but more powerful driving.
Also, as its name specifies, a 4WD system powers all four wheels when needed. Because the engine is sending power to all four wheels instead of two, the vehicle might feel slower. Fuel consumption might also increase.
The benefit is that all four wheels are turning with increased torque. Therefore they can grip the terrain better. But, driving with the 4WD mode on requires some precautions. Let’s discuss them in the following section.
Cautions you must take with the Sierra 4WD
First of all, if you’re not facing rugged terrains, you must drive in Two-High. It’s unnecessary to active any other mode, as it can lead to transmission damages.
If you come to slippery terrain, like ice, snowy and muddy roads that aren’t deep, you activate Four-High. The engine is now sending power to the rear and front axles, allowing for better traction. Remember that the GMC Sierra can shift between these two modes on the fly.
But, if you’re driving and come across deep mud, snow, or water, you need as much torque as possible. So, stop the Sierra completely, shift into neutral, and engage the Four-Low option with the knob on your controls.
You will feel your vehicle move slower but with much more responsiveness to the throttle. Navigate your terrain with slow speed, as there is no need to hurry. Accelerating will only cause the tires to lose friction.
Because all your tires turn with equal amounts of torque, they can’t use the same speed as you would with Two-High engaged. If the terrain is slippery, you should be fine. But, if you have adequate grip, then you might add stress to the steering and transmission.
This next caution doesn’t directly relate to 4WD, but always remember to use your brake pedal sparingly. Any stops you do in conditions with low friction will accentuate.
The car might slide more, or it even could lose all traction because the wheels have stopped moving. Especially in decent, do not jam on the brakes aggressively.
Do not use Four-Low on asphalt. It will cause the tires to move at an equal pace when you don’t need to. So, if the conditions improve, it’s best to shift back to Four-Low.
If you’re crossing a body of water, be sure to check the depth beforehand. When crossing a river or a pond, be sure to use a constant speed to generate awake in front of your car. Do not stop unless it’s indispensable.
Finally, replace the transfer case fluids every 45,000 miles or the equivalent in months. An adequately lubricated transfer case will go for many miles.
Now that we’ve seen some of the cautions to take with 4WD, let’s discuss which GMC Sierra models come with 4WD.
Which Sierras come with 4WD?
|4WD as optional
|4WD as Standard
GMC offers an optional 4WD on its three most basic trim levels, the SLE, Elevation, and SLT. These are options for those looking for a luxury truck that can do hard work from time to time.
The AT4, on the other hand, is an all-out offroading trim level. IT only comes with 4WD and other extras to make it more capable in the most challenging terrain.
The top-of-the-line Denali is the opposite. This Sierra doesn’t come with 4WD, not even as an option. It’s designed for urban driving and occasional towing as well.
The GMC Sierra Heavy Duty, known as the 2500/3500, comes with 4WD as optional in all its trim levels, including the Denali. Only the AT4 comes with no option for 2WD.
What are some common problems with 4WD?
The GMC Sierra is reliable. But recent surveys from Consumer Reports and JD Power have found some issues with components such as the transfer case.
AT about 150,000 miles, users have reported that the Transfer Case Position Sensor fails. This can lead to the truck being unable to shift from High to Low and vice versa. Also, some have reported that, past 130,000 miles, the seals in the transfer case tend to leak. This can eventually lead to faulty lubrication and damaged components.
Others have reported that the knob that helps shift between 2WD and 4WD is prone to failure, either by braking or jamming.
In general, the GMC Sierra has had lower reliability than expected in the past seven years. Though its running cost is average, its reliability places it at a lower tier than the competition.
Many users out there have asked how to engage the 4WD on the GMC Sierra. Thanks to its automatic transfer case, it’s easy to do.
The GMC Sierra comes with a knob on the driver’s side that quickly engages Four-High and Four-low, with just a twist. The Sierra comes with varying modes that help the driver tackle different terrains such as snow, mud, ice, and water.
If you lose some grip, then Four-High is ideal because it sends power to all four wheels, but you can change it on the fly.
When the going gets rough, you have to stop and shift into neutral. Only then can you engage the Four-Low gear. This will give you added torque on both the rear and front axles. Use this only with deep mud or snow or while crossing water.
But, 4WD comes with its own set of cautions. Be sure to use it only when you need it and not in the conditions like asphalt. Turning with 4WD engage can cause excessive stress on the axles and lead to premature damage.
Finally, when driving with the 4WD engaged, you should take all the precautions necessary for safe driving. Hopefully, this article provides the information to use your GMC Sierra’s 4WD and enjoy it, which is the most important thing.