AWD/4WD

Importance of inspecting AWD and/or 4WD a used car:

     All wheel drive and 4 wheel drive are essentially mechanisms that allow all 4 wheels to spin, instead of 2 as it is on regular cars. All wheel drive usually implies that all 4 wheels are engaged at all times and you cannot disconnect the other two, while 4WD on the other hand means that you can disconnect the other 2 wheels if you want. Checking the proper operation of 4WD system might help you down the road when you really need to use it.

What to look for when checking AWD and/or 4WD?

     First of all, you have to check for leaks, as cars with AWD/4WD have more than one differential. It's rather hard to check for leaks unless the car is up on the lift, but if the car is an SUV and has high clearance, you can peak underneath and see if you can find differentials (they are round casings between axles and sometimes in-between axles).

     On AWD car you have to listen for clunks, whining and grinding that is generally associated with suspension problems. If you find any suspension problems with an AWD car it's best to avoid it, since it can be very costly to repair and differential/axle problems.

     On 4WD car you have to check if the other 2 wheels engage properly. You can do this by first getting a feel of how the car drives with 2 wheels, then engage the 4WD move and drive around. If the system is engaged, the car should become more "sluggish", since the engine is working harder now to spin all 4 wheels, instead of just 2. You generally should feel or hear some sort of mechanism working as you switch the 4WD mode on and the motor engages the 4WD mode. If nothing is happening when you move the lever and the car feels absolutely the same, then there is a possibility that 4WD system is not working. Troubleshooting it is going to cost quite a bit of money, this it's better to avoid such car.     

Conclusion:

     Inspect differentials for leaks, listen for any grinding, whining or clunks during the test drive. Check for proper engagement of 4WD by test driving the car before and after engaging the 4WD mode. The car should feel more sluggish.