Should I drive in 4H or 4L mode? Can I switch from 2H to 4H while driving? Will 4H mode affect my fuel economy? These are just some of the questions regarding the 4-wheel drive system you'll find on many trucks and SUVs.

With multiple features, the average 4WD system on an SUV can come across as quite daunting to the uninitiated user. However, the truth is that each option has its own specific use case, and when you're aware of what they are, you'll know precisely what to engage when. This article will help you familiarize them before you find yourself in a sticky situation.

Understanding What it Means to Have 4 Wheel Drive

Before we dive into the specifics of what each mode has to offer, it'll help to know how a 4-wheel drive system works. As the name implies, a 4WD system will distribute power from the wheel to all four wheels, improving traction in several scenarios. Power from the engine is transferred to the transmission, then a transfer case. The transfer case sends torque to the wheels, and which wheels receive torque can be controlled in the cab. A driveshaft spins between the transfer case and the front axle and a separate one sends power to the rear axle from the transfer case.

This can be particularly useful in low-grip conditions, like when it's snowing, when there are steep inclines, or when you're off-roading and not all wheels are in constant contact with the ground surface.

Most SUVs come with part-time 4-wheel drive systems, while some utilize a system that sends power to all the wheels all the time. When you're not engaging 4WD, the engine will send power to either the front or rear wheels like on a conventional 2WD system.

It's worth noting that not all 4WD systems are made the same. Plus, most of them will come with multiple modes, with the most common being 4H (high), 4L (low), and Auto, each with its own specific uses.

When to Use Auto (Automatic)

The Auto (Automatic) function on your 4WD vehicle is most suitable for everyday driving conditions where you might occasionally need a little extra traction. In this mode, your car will function in 2WD mode and automatically engage 4WD when it senses a loss in traction. So, if your car's wheels start to slip on an icy or slippery road or in mud, a signal will be sent to the ECU, prompting it to send power to all four wheels.

When to Use 4H (High)

When driving conditions are slightly more demanding, like through sand or deep gravel, you'll benefit most from switching to 4H mode. In this mode, power is sent to all four wheels, allowing for relatively high-speed driving. So, if you're carrying speed down a trail or up a slope, switching to 4H will give you better traction.

Keep in mind that using 4H mode when you're driving on tarmac or on the highway can cause additional wear to the transmission, tires, and the rest of the drivetrain, so it's best saved for when you really need it.

When to Use 4L (Low)

You should switch to 4L mode only in extreme off-roading situations, like while traversing across rock formations or if you're towing an extremely heavy load over a short distance. In this mode, the transmission adopts a shorter gearing, multiplying torque sent to the wheels. Contrary to popular belief, engaging 4L mode in wet mud or slush may not be the ideal solution since the added torque sent to the wheels might cause them to spin and dig into the ground.

In some cases, the 4L mode also locks the differential, increasing your chances of getting out of a tough spot when one wheel on an axle is not making contact with the ground. Because of its specific use case, 4L mode should only be employed in situations where speeds are extremely low — under 10mph is a reasonable threshold. Engaging it otherwise could damage the gearbox.

Cardinal Rules of Operating a Vehicle with 4 Wheel Drive

Now that you're familiar with the different 4WD modes, you should know which works best in a given situation. Aside from the functionality of the different modes, there are some other rules to keep in mind if you want to avoid getting stuck or causing damage to your vehicle. So, before you head out and tackle your next adventure, ensure you're aware of the following:

Engage 4WD Before You Need it

By doing so, your vehicle and you are better equipped to traverse through a challenging situation rather than finding yourself stuck in the middle having to change modes. It's better for the vehicle and will let you focus on just driving.

Don't Employ 4WD on Tarmac

There are exceptions to this rule, but your 4WD system is generally designed to help in off-roading situations. Having it engaged for long periods on the highway or while you drive around town can strain the gearbox and drastically affect your fuel economy.

Know Your Vehicle's 4WD System

The owner's manual is the best place to learn about your vehicle's 4WD system. You should find basic information on a sticker in the car (usually by the gear lever or the inner edge of the door frame). However, we still recommend that you read the detailed information the manufacturer has provided in the manual.

You should find information on what modes the manufacturer recommends for different scenarios, how you can change between modes, and if there are any other features (like traction control or dedicated ‘Snow', or ‘Off-Road' modes) that will improve your vehicle's off-road abilities.

On most modern SUVs, you should be able to switch from 2H to 4H mode on the fly, given you're below a certain manufacturer-recommended speed. However, that's unlikely to be the case with switching to 4L mode. You will have to come to a complete halt before you do so, or you can cause irreversible, expensive damage to the drivetrain.

A 4WD system can significantly improve the vehicle's off-road capabilities and, consequently, your experience. Use it right, and it should come in handy more times than once. Misuse it, and you could end up causing some severe damage. With the information above, you should be able to avoid any issues and utilize a 4WD system to the maximum.