Suspension - Cracking, Knocking or Thumping Noises
Date: November 27, 2006Order No.: T-B-32.22/45
Supersedes:
Group: 32
SUBJECT:
Model 164.122/175/186
Model Year 2006
Up to Series Production 04/2006, Equipped with Airmatic Suspension
Cracking, Knocking or Thumping Noise From the Front Axle Area
If you receive customer reports in the above model vehicles of a cracking, knocking or thumping noise from the front axle area of the vehicle during moderate or high acceleration from a standstill, perform the following test procedure.
NOTE:
This condition only affects vehicles with Airmatic suspension (code 489)
1. Ensure that the Airmatic suspension level and ADS damping is set to "Normal" (no LEDs illuminated on switches). Accelerate the vehicle from a standstill with a moderate or high acceleration rate too approximately 10 mph. The knocking or thumping condition will be evident at approximately 5 mph.
2. Switch the Airmatic suspension ADS damping to "Sport" mode ("Sport" LED illuminated on switch), but ensure that the Airmatic suspension level is set to "Normal" (no LEDs illuminated on switch). Accelerate the vehicle from a standstill with a moderate or high acceleration rate too approximately 10 mph. If the knocking or thumping condition is no longer present, then replace the Airmatic control module with a revised version. Reference WIS document AR32.22-P-6000GZ. If the knocking or thumping noise condition is still present, then further conventional diagnostics needs to be performed in order to isolate the origin of the noise.
NOTE:
When the vehicle is accelerated briskly, the Adaptive Damping System (ADS) of the Airmatic suspension regulates the air suspension's dampening levels. The sudden pressure steps occurring during the dampening process may lead to the noises. If "Sport" mode or an increased vehicle level is selected, the ADS valves do not switch (passive mode), which results in the absence of the noise.
This bulletin has been created and maintained in accordance with MBUSA-SLP S423QH001, Document and Data Control, and MBUSA-SLP S424HH001, Control of Quality Records.
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