Mercedes-Benz bulletin LI35.31-P-080353

Complaint Whining / humming noises (described as foghorn‑like) from the drivetrain in the rear axle area during cornering. (figure 1) On the above‑mentioned vehicles with a mileage up to 15,000 km (about 9,300 mi), noises can occur from the rear axle differential. Cause Drivetrain resonance caused by the gear mesh of the ring and pinion in the rear axle differential in combination with installed damper elements on the axle shafts. Remedy For precise noise analysis and localization, use the chassis ear/NVH kit and the following driving procedure: 1. Drive the vehicle in a tight circle with the steering at full lock in both clockwise and counter clockwise directions. ‑ Vary engine load during the maneuvers If a foghorn‑like noise occurs comparable to the reference video, the vehicle exhibits the condition If the noise is present: 1. Add 15 ml of additive (Friction Modifier) into the rear axle differential via the filler plug IMPORTANT NOTE: Do NOT use Friction Modifier in vehicles equipped with an electronically controlled locking differential (Code 467). 2. Tighten the filler plug 3. Drive the vehicle until the rear axle differential reaches operating temperature Note: Proper activation of the additive requires elevated oil temperatures After the test drive to operating temperature, evaluate the noise when the rear axle is cold and when warm. If the noise is no longer present: The issue is resolved and the vehicle can be released. If there is noticeable improvement: The vehicle can be released with the explanation that the noise will gradually disappear over an extended driving distance. If the noise is still present and remains unchanged: Replace the rear axle differential.

Owners of the 41 model years this bulletin names have filed 930 complaints with NHTSA since 2015. 52 of them name Power Train — the same broad component group this bulletin is filed under. NHTSA groups complaints coarsely, so that means the same area of the vehicle, not necessarily the same fault.