Mercedes Active Body Control Suspension Issues Explained(+Top 3 Problems)

In this brief article we are going to discuss the different Mercedes Active Body Control Suspension problems, what the causes are, and Troubleshooting Tips.

What are the most common suspension issues in the Mercedes Active Body Control(ABC)? 

The most common Mercedes ABC suspension issues are:

  • “ABC Drive Carefully” or “ABC Visit Workshop” 
  • Rodeo Test not Working
  • “Drive Carefully” message when hitting a speed breaker or pothole
  • ABC Warning during Cornering
  • Corner Sagging when parked
  • Whine Noise
  • “Drive Carefully” or “Visit Workshop” appears on startup
  • Whistling or Hissing Noise

What is Mercedes Active Body Control (ABC)?

Active Body Control, popularly known as ABC, is the brand name that Mercedes-Benz uses to describe its proprietary “Hydraulic Fully Active Suspension” system. The ABC Module computer detects body movement by signals from sensors located throughout the vehicle, and accordingly reacts and controls the action of the active suspension using Hydraulic Servomechanisms. 

The ABC suspension was first made available on Mercedes-Benz CL-Class (C215). Subsequently ABC was available on cars belonging to the W216, W220 & W221 chassis platform models. The models that were built with ABC would have the Build-CODE 487 to distinguish themselves.

How to Deal With Suspension Problems in the Mercedes Active Body Control?(+7 Troubleshooting Tips)

“ABC Drive Carefully” or “ABC Visit Workshop” Error

  • The Color of the message text is also important 
    • White or Blue means that the warning is not critical, and you should be able to continue driving. 
    • Red indicates a critical problem. It is unsafe to continue driving the car. If you continue and if vehicle height drops to an unacceptable level, the car will display a “Stop, Vehicle Too Low” warning. Driving beyond this point might lead to expensive repairs
  • The ABC system may have locked the struts at the Normal position if it detected a critical error. 
  • Due to the fluid circulation having stopped, the Ride Quality turns bouncy and rough

Root Causes:

  • A loose electrical connection
  • ABC sensor failure
  • ABC pump failure
  • ABC system Leak
  • ABC low hydraulic fluid level

Pro Tips

  • If the ABC warning message only appeared when you turned on the ignition and then turned off, the problem could be due to a pressure drop. Once pressure builds up, the ABC warning may turn off. 
  • If the ABC warning message persists, then there could be a more serious problem with the ABC system. For Further analysis you will need to read the ABC module Fault codes with a Mercedes-Benz scanner. 

Rodeo Test not Working

  • If there are active fault codes on the ABC module pointing to low pressure then it does not start the Rodeo test. You would need to read the codes to find out what the actual fault is.
  • On Diagnosis, if you get  the fault code “B4/5 ABC pressure sensor 0 bar” and no action, then 
    • The ABC pump may be faulty or 
    • There might be no hydraulic fluid present due to a major leak somewhere in the system.  

“Drive Carefully” message when hitting a speed breaker or pothole

If this happens when you hit a speed bump, the problem usually points to 

  • A malfunctioning accumulator that fails to provide instant pressures as and when needed or
  • A loose electrical connection. 

Troubleshooting “Drive Carefully”

  • Check the ABC fluid level. See if it keeps dropping after you refill it. If it does, then one of the accumulators could be leaking hydraulic fluid. 
  • The ABC reservoir may be overflowing with hydraulic fluid
  • ABC accumulators have an average life of ten to twelve years. Once an accumulator fails, it leads to all the actuator failures. Hence, it is recommended to replace all the Accumulators at the same time once every 8-10 years even before they actually fail. This could potentially yield savings in maintenance costs down the line.

ABC Warning during Cornering

  • On some occasions, during the event of hard cornering or hard braking, the ABC warning message may appear briefly.
  • This indicates that the system is unable to meet the pressure demand. 

Probable Root Causes are:

  • Low pressure detected at the ABC pump 
  • One or more failed accumulators
  • Low hydraulic fluid level probably due to a leakage

Corner Sagging when parked

  • In cars that have ABC, it is usual for one of the corners to lower or sag when the vehicle is parked for a long period like a couple of weeks.
  • Ideally, this should not happen if the vehicle was parked for only a couple of days. 
  • In both cases, ideally, the vehicle Ride Height should rise to the normal level after the engine is started. 

Root Causes for Corner sagging when parked: 

  • The valve block is unable to hold pressure. The O-rings in the valve block can wear over time which gradually leads to hydraulic fluid escaping from the strut. It is possible to rebuild the valve block with a repair kit
  • The Struts may have a slow leak. 
  • A filter in the ABC reservoir that has become dirty and needs replacement

Whining Noise

  • Humming or whining Noise at low engine RPMs.

Root Cause for Whining Noise

  • The most probable cause would be a Worn-out Pulsation Dampener. 
  • On the SL-Class, the Pulsation Dampener is mounted right behind the front LH wheel well
  • On the S/CL Class, the Pulsation Dampener is attached to the undercarriage by the transmission. 
  • On model year 2007 onwards, the Pulsation Dampener has become part of the ABC pump itself.

“Drive Carefully” or “Visit Workshop” appears on startup

  • Either the “Drive Carefully” or “Visit Workshop” warning message appears in the display when the car is started and does not go off throughout the time of vehicle running

Root Causes

The “Drive Carefully” or “Visit Workshop” warning problem may be caused by one of the following reasons: 

  • ABC pump – If the ABC Pump is not generating enough pressure it gives out a warning message. The pump may generate enough pressure later after a restart, and the message might go away. But there is every possibility that the warning might come back after driving for a while. 
  • Hydraulic Fluid leakage – one most common issue and reason for the Warning is Loss of Fluid due to a leakage somewhere in the system. Generally, ABC fluid leaks are easy to identify. Root cause for leakage is Rust in the ABC hoses.
  • Air trapped within the system can also trigger the ABC warning message. The easiest way to fix this problem is by pressuring the system and doing a RODEO test.
  • Level sensor – A faulty ride height sensor could also cause the ABC Warning message. 

Troubleshooting the “Drive Carefully” or “Visit Workshop” warning 

  • The ABC pump may require some amount of priming in order for it to operate normally once again. This is done by using either a Mercedes-Benz or a compatible aftermarket scanner to instruct the system to pressurize the reservoir and get the hydraulic fluid circulating once again.
  • Inspect the underside of the chassis for any signs of hydraulic fluid leak. For this you may need to remove the splash shields under the vehicle.
  • If you find out that the problem is not leak-related, the next step is to read the diagnostic trouble codes (DTC) from the ABC Control Unit and infer the component in  the system that is faulty. 
  • While reading the DTC if you find out that the pump is faulty, you will get a code indicating that the ABC pump cannot generate enough pressure or pressure maybe ‘0’.
  • In order to confirm that the Pump is at fault, you can test the ABC pump using the diagnostic tool and monitor the pressure as you perform a RODEO test. 
  • For a properly working pump, during the RODEO test, the pressure must always stay above 100 psi. If the pressure drops below 100 psi, you could conclude that the pump may be too weak and needs to be replaced. 

Whistling or Hissing Noise

  • The source of the Whistling and hissing noise can come from would most probably be the valve block.  
  • This would happen if there is air trapped within the hydraulic lines. 
  • Most commonly, the Valve Block is located at the front left corner behind the bumper or behind the rear wheel well. 
  • In order to bleed air out of the system the procedure is to run the Rodeo Test. In the Diagnostic Tool, you can do this by going to “Control Units” -> “ABC Control Unit” -> “Activations” -> “Rodeo Test”

Conclusion

In this brief article we have discussed the different Mercedes Active Body Control Suspension problems, what the causes are, and Troubleshooting Tips.

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