2011 Mercedes ML-Class Owner's Manual - Page 198

196 Off-road driving systems Differential lock General notes i Differential locks are available only in vehicles with the Off-Road Pro engineering package. Your vehicle is equipped with the following: RA differential lock for the transfer box: this controls the balance between the front and rear axles. RA differential lock for the rear axle: this controls the balance between the wheels and the rear axle. Differential locks improve the vehicle's traction. 4ETS (Y page 67)controls the balance between the wheels on the front axle. Information on "Off-road driving"; see (Y page 166). Information about the differential and differential locks When the vehicle is driving around a curve, the wheels on the outside of the curve have to cover a greater distance and therefore have to turn faster than the wheels on the inside. The differential, a transmission in the drive train, balances these different rotational speeds out, making cornering possible. The disadvantage of a differential: the wheels with the least grip are driven the hardest. Example: one wheel on a driven axle is on a snow-covered surface and therefore has no traction. This wheel has the most driving force, since the differential distributes most of the force to the wheel with the least resistance. The wheel on the opposite side of this axle, which is on a solid surface and could therefore enable traction, does not have any driving force. 4ETS eliminates this disadvantage and ensures good steerability by braking the spinning wheel automatically and thereby directing more force to the wheel that is on a solid surface and can provide traction. ESP® and 4ETS are traction systems that are ideally suited to road driving and driving on easily negotiable off-road terrain. The LOW RANGE off-road gear also improves off-road capability. Difficult off-road conditions require additional measures, such as locking one or more differentials. Your vehicle has two differential locks: one (central) differential lock for the transfer case and one differential lock for the rear axle. Both differential locks can be activated using the selector wheel on the center console. When the (central) differential for the transfer case is locked, the speed of the front wheels is the same as the speed of the rear wheels. When the differential for the rear axle is locked, both of the rear wheels turn at the same speed, independent of their individual torques. Note that activating the differential locks significantly reduces the steerability of the vehicle. For your safety, the safety of others and to prevent damage to the vehicle, the differential locks must not be activated on paved roads. Note that the differential function is necessary when driving on paved roads and that the differentials must never be locked on paved roads. Otherwise, the vehicle can no longer be steered. The differential locks must therefore only be activated when driving off-road, and then only if activating the other driving systems (4ETS, ESP® and LOW RANGE off-road gear) is no longer sufficient. Driving and parking Engaging the differential locks ! Drive off slowly when the differential locks are engaged. Function or performance tests may only be performed on a 2-axle dynamometer. If you wish to operate the vehicle on such a dynamometer, please consult an authorized Mercedes-Benz Center beforehand. You could otherwise damage the drive train or the brake system.