Suspension - ABC Suspension Humming/Buzzing Noise

HUMMING/HOWLING NOISE FROM ABC SUSPENSION UP TO APPROX. 2000 RPM

Topic number LI32.50-P-048280

Version 1

Design group 32.50 Active body control (ABC)

Date 11-10-2009

Validity MODEL 215, 216.37#, 220, 221, 230 with code 487
(ABC); all vehicles with Active Body Control (code 487)

Reason for change Validity extended to current model series / Supersedes DTB P-B-32.50/24

Reason for block

Complaint:

Humming / howling noises can be heard from underfloor area.
Noise can be heard from idle up to approx. 2000 rpm. Above this, it is drowned out by the engine noise.

Note:
The noise is particularly noticeable at approx. 1400 rpm.

Cause:

As mileage increases (>100,000 km / 62,000 miles), the gas pressure in the pulsation damper ("pressure reservoir" / "damper") of the ABC system can decline, meaning that the full damping effect may no longer be available.

Note:
Noises may also be caused by touching/stressed ABC lines. Please check this before replacing any parts, and correct if necessary.

Aids:

Use clamp kit for noise diagnosis (STEELMAN ChassisEAR) as per WIS document (AR32.00-P-2000A).

Remedy:

If ABC lines are not touching / stressed,
replace pulsation damper at pressure supply valve block (ABC I) or at tandem pump (ABC-PLUS).

Note:
Pulsation damper can be replaced separately, sealing ring is included.

Note:
Replacement of the entire pressure supply valve unit or ABC tandem pump is not required.

Note:
With the introduction of ABC-PLUS (as of model year 2006), the pulsation damper is located on the tandem pump.





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Symptoms





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Work Units





WIS-References








Validity





Attachment - Pulsation damper: No. 410





Attachment - Pulsation damper: No. 290 Valid up to model year 2006





Attachment - Pulsation damper: No. 15