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· Registered
3 Posts
Discussion Starter · #1 ·
I have a persistent noise under my hood. It sounds like a hydraulic pump that is out of fluid. It only comes on when the car is moving or started cold in the morning. When you slow down and come to a stop the noise goes away. It starts again when you get going again.

At first we thought it was the fan motor assembly so we replaced the unit. The noise was still there. Next we replaced the fuel pump. The noise is still there. I am at wits end! What could it be?

Is there a hydraulic pump that controls leveling on the car? The car does not look unleveled. I seem to remember something about the car actually lowering its profile during driving. Could this be the issue?

I need help!

Jim Buggie
[email protected]

· W221 & Audio Moderator
2015 S550
11,244 Posts
If your car has an ABC (Active Body Control) suspension (you have ABC if you have a button on your dashboard that says "ABC - Sport." If you have a button with a shock absorber depiction and curved arrows on each side, you have Airmatic) it could be a hydraulic pump, depending on your suspension system.

ABC is a computer-controlled hydraulic system; Airmatic is pneumatic, without the computer controls. ABC has a hydraulic pump, and airmatic has a pneumatic pump.

In either case, before you throw more money away guessing at the problem, I suggest you have an MB tech diagnose the problem. Whether it is ABC or airmatic components, they tend to be expensive.
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