AWD and 4WD both send power to all four wheels. They do it in different ways, and the difference changes how you should drive one and what you should check before you buy one used.
The short answer
- AWD works by itself, with nothing for you to switch on. It is built for paved roads in all kinds of weather. You find it on many crossovers and cars.
- Part-time 4WD is a switch. You turn it on for dirt, gravel, mud, snow or sand, and you turn it off on dry pavement. It is the usual system on 4WD pickups and traditional SUVs.
- Full-time 4WD sits in between. It can stay on, on any road, and many versions add a low range and a lock for rough ground.
Not sure which one you have? Look at the 4WD selector, the badge, or the owner's manual.
Part-time 4WD, and why it stays off dry pavement
When you shift a part-time system into 4WD, the front and rear driveshafts are locked together, so they turn at the same speed. There is no center differential to let them turn at different speeds.
That lock is what gives part-time 4WD its grip on loose or slippery ground. It is also why it does not belong on dry pavement. In a turn, the front wheels trace a wider arc than the rear wheels, so they need to turn a little faster. On dirt or snow, the tires slip a little and the difference goes away. On dry pavement the tires grip too well to slip, so the strain builds up in the driveline instead. Drivers call it binding. You can feel it in a tight turn: the front end hops, the tires scrub, and the steering fights you.
The owner's manuals say the same thing. Ford's manual for the 2019 F-150 says not to use 4H or 4L on dry, hard-surfaced roads. Ram's 2022 heavy-duty manual warns that driving in 4WD High or Low on dry, hard-surfaced roads "may cause increased tire wear and damage to the driveline components." Toyota's 2026 Tacoma manual says to use 4H only where the tires can slide, "like off-road, icy or snow-covered roads."
So use it for the mud, sand or snow, and shift back to 2WD when you are on dry road again.
Over time, binding loads the parts that carry the power: the U-joints, the driveshafts, the transfer case, the front differential and the CV joints.
The trap on some trucks: Auto 4WD
Many newer trucks have an automatic 4WD setting on the same dial as 4H. Ford marks it 4A. They are not the same thing. In Ford's 2018 Expedition manual, 4A sends power to the front and rear wheels as needed for traction, while 4H is not recommended on dry pavement.
Same truck, same dial, two different rules. Check which one is on, and check your manual for what your truck's auto setting allows.
Full-time 4WD
A full-time system has a center differential, so the front and rear can turn at different speeds. That is what lets it stay on, on any road.
Many full-time systems also have a center differential lock and a low range for rough ground. Locking the center ties the front and rear together again, so treat it like part-time 4WD: lock it on loose or slippery ground, and unlock it for normal driving on dry roads. Your owner's manual will say how.
AWD
AWD is built for the road. It works without you doing anything, and turning on pavement is exactly what it was designed for. Most AWD systems have no low range, so they are not made for serious off-road driving.
The one thing AWD asks of you is a matching set of tires. A tire that is much more worn than the others, or a different size, turns at a different speed, and the system keeps working against it. Ford's manual for the 2021 Edge recommends replacing all four tires, rather than mixing badly worn tires with new ones, to avoid damage to the AWD system.
Which is better?
Neither, in general. It depends on where you drive.
- If you mostly drive paved roads, in rain and the odd cold snap, AWD does the job and asks nothing of you.
- If you tow up a wet boat ramp, drive on sand or dirt, or go off-road, 4WD, with its low range, is the better tool.
Buying a used 4WD or AWD: what to check
A driveline that has been worked hard does not always show it on a short drive. These are worth checking before you buy:
- Shift it in and out. Ask the seller to shift into 4WD and back while you watch the dash, on gravel or dirt if you can, with the wheels straight. On many trucks the 4WD light flashes while the shift is happening and goes steady when it is done. Ram's manual says the light "will flash until the transfer case completes the shift." A light that keeps flashing, or a truck that will not shift back to 2WD, is worth asking about.
- Listen. A grind or a clunk when it shifts. A growl or a whine that rises with speed. A clicking in a slow, tight turn, which can point to a worn CV joint.
- Look underneath. Wet spots or fresh drips around the transfer case and the differentials, and torn CV boots, the rubber covers on the front axles.
- On AWD, look at all four tires. Same brand, same size and similar wear. A mismatched set can mean tires were replaced one at a time.
- Ask how it was used. Towing, off-road, beach driving. None of it rules a car out on its own, but it tells you where to look.
Where we come in
You do not have to crawl under the truck yourself. One of our certified technicians comes to the car, on a dealer lot or in a seller's driveway, across the Atlanta and Orlando metro areas. You do not need to be there.
Every level includes the mechanical and safety inspection, the underbody and structural review, where the technician looks for leaks, damage and wear underneath the car, the brakes, suspension and steering, and a dealer-level diagnostic scan, whose depth varies by make and year. We road test the car when the seller allows it and it is safe and legal to drive.
Want the 4WD looked at closely? On Enhanced (up to 3) and Elite (up to 6), you name your Areas of Concern when you book, such as the 4WD or a noise the seller mentioned. Your inspector gives each one a closer look and answers it in writing in your report.
Essential and Enhanced reports arrive within 24 hours of the inspection, and most go out the same day. Elite reports arrive by 11:59 PM Eastern on inspection day, or we refund $99.
For a full walk-around of any used car, use our used car inspection checklist, and our 10 used car red flags.
Questions we get
Can you turn in 4WD on pavement? On AWD, yes. On full-time 4WD, yes, as long as the center differential is not locked. On part-time 4WD, keep it for loose or slippery ground, and shift back to 2WD on dry pavement.
Is AWD the same as 4WD? No. Both drive all four wheels. AWD runs on its own and is made for the road. Part-time 4WD is switched on by the driver for rough or slippery ground, and full-time 4WD sits in between.
Is a used 4WD truck a risk? Not on its own. Plenty are well looked after. Check the points above, and get the truck inspected before you pay.
Book an inspection
Inspections start at $259. Book an inspection, or text or call 833-644-0800 and we will help you pick the right level for the car.