When you bring your vehicle to a Motor Vehicle Inspection Center (MVIC) for inspection, some of the new tests involve driving it on a rolling road. Vehicles undergoing inspection will use the rolling road for the brake test, speedometer test, and the side-slip test.
If your vehicle happens to be front-wheel-drive (FWD) or rear-wheel-drive (RWD), then running on the rolling road shouldn't be an issue. However, it might be a problem for vehicles with four-wheel-drive (4WD)/all-wheel-drive (AWD).
As you can see from the MVIC we visited, there is only one pair of rollers mounted onto the facility floor. If you run a vehicle with permanent or full-time 4WD or AWD here such as Subarus or BMWs with xDrive, then odds are the system will break. Full-time 4WD/AWD vehicles require all four wheels to run at the same time. Otherwise, the center differential will malfunction and break.
MVICs do have an extra pair of rollers should that be the case. With that said, you should inform MVIC inspectors that your vehicle is 4WD or AWD before undergoing the test. This way, they can bring out an additional set of rollers before your vehicle is placed on the rolling road if needed.
If you happen to be driving an SUV or pick-up truck with a selectable 4WD system, then putting it into 2WD mode should allow you to run only the rear-wheels without any problem. Additionally, if your vehicle has traction control, it should be turned off before undergoing the test as well.
While we expect the technicians to know whether the vehicle has permanent AWD/4WD, that isn't always the case. Subsequently, they handle various cars every day and might not be too versed with some makes and models. So, telling them that your vehicle is 4WD/AWD beforehand can save you from troubles and complete the MVIC test without issue.