All-wheel drive (AWD) and four-wheel drive (4WD) essentially mean the same thing, and the only difference is that four-wheel drive tends to refer to an optional drive system whereas all-wheel drive is a full-time system that cannot be turned off. What these systems are used for is to increase traction control, which is especially useful for offroading and driving on icy or snow-covered surfaces.
When there is snow on the road, a car with two-wheel drive will have difficulty because each tire only gains a small amount of traction, but switching over to 4WD will allow a vehicle to deliver additional force to each tire, which will increase the friction between the vehicle and the roadway so you can keep driving.
Since winter is coming up, it can be a good idea to make sure that the drive system is functioning properly to ensure safer driving in slippery conditions. Whether your vehicle has AWD or 4WD, the checklist for diagnosing problems is the same.
The first thing you should do is listen for unusual sounds. Engage 4WD and drive the vehicle slowly, paying close attention for any unfamiliar or unnatural noises or vibrations. You should also watch the RPM gage on the dash. if the needle rises quickly while you are traveling at low speeds, the mechanism that transfers your vehicle's drive system to 4WD is operating normally.
The best way to make sure the drive system is delivering the proper amount of torque to each individual wheel and functioning properly is to put it through a real-life test. Driving the vehicle on hills, muddy or icy surfaces can help you determine if the tires act the way they're supposed to in this driving mode. Just be sure to find a relatively safe location for this part of the test, or at least have a friend present.
In this test, the front tires should spin faster than the rear tires without affecting the overall speed of the vehicle. This is how the tires find traction on low-friction surfaces.
If your vehicle does not pass one or any of these tests, it may be time to conduct more thorough diagnostic investigations, as a faulty 4WD system can make driving even more dangerous this winter.
It is also important to note that 4WD will not necessarily facilitate stopping on slippery surfaces any more than two-wheel drive would.