The Definitive Guide To The Mercedes-Benz AIRMATIC Suspension System

Throughout the last twenty years, Mercedes-Benz has equipped numerous vehicles in its lineup with air-ride from the factory. Although complex, this system shouldn't be feared; it's broken up into relatively easy-to-service components.

Introduced on the W220 S-Class for the 2000 model year, Mercedes-Benz began equipping various models in its lineup with an air-suspension system dubbed "Mercedes-Benz AIRMATIC." This system replaced the traditional coil springs found on cars before this time with air springs with electronic level control and adaptive damping at all four corners. The combination of adaptive damping that adjusts based on road quality and driving style, in concert with air springs, makes for an extremely comfortable ride.

Mercedes-Benz CLS-Class (W219)

• CLS500: 2006
• CLS55: 2006
• CLS550: 2007-2011
• CLS63: 2007-2011

Mercedes-Benz Airmatic Benefits & Features

You might be asking why you would want such a complex system instead of the much simpler coil-spring setup. There are several reasons, some of which make it well worth it over the traditional coil-spring suspension.

• Auto-Leveling—Auto leveling compensates for additional passengers or cargo in your car. Not only does this make your car look better cruising down the highway, but it keeps the handling dynamics exactly how the engineers designed it, no matter how much weight or where it's added. 
• Auto Height Adjustment—When reaching highway speeds, the car automatically lowers itself to improve aerodynamic efficiency. This results in a more stable car at highway speeds and improves fuel economy. 
• Axle Lift - Have you ever seen low cars scrape their front end on rough roads, speed bumps, or steep driveway entrances? Mercedes-Benz combats this common issue by allowing you to raise the front axle to clear obstacles.  
• Selectable Driving Modes—The driver can select between three distinct driving modes: Comfort, Sport 1, and Sport 2. Depending on your style, Comfort and Sport 1 are both great for street driving, whereas Sport 2 is more suited for perfectly smooth roads or on a track. 
• Adaptive Damping—This is one of the most advanced parts of the whole system. Under hard acceleration, the system reduces axle lift, and under hard braking, it reduces the amount of nosedive. This makes for a more comfortable driving experience and greatly improves the handling characteristics. 
  • The damping profile/driving modes will auto-adjust from "Comfort" to "Sport 1" when driving over 100MPH, and based on calculated horizontal acceleration. 

Mercedes-Benz Airmatic System Components

Airmatic Control Module

This is the brain of the system. It uses inputs from the ECM, ESP module, transmission module, instrument cluster, steering angle sensor, acceleration sensors, and the level/damping switches in the cabin, among others. 

As an example, the module can use braking torque or engine torque values to determine when to switch the damping valves and reduce body roll. These adjustments can be performed in milliseconds, which is especially helpful during emergency maneuvers.

Mercedes-Benz CLS-Class & E-Class

The Airmatic control module is located in the passenger compartment right side footwell. You will need to pull back the carpeting to access it where it is mounted on a plate.

Instrument Cluster

You wouldn't think so, but the instrument cluster plays a vital role in the AIRMATIC system. The cluster provides warnings for when the vehicle is too low, as well as an indicator that the car is rising and the current damping levels. This is your first sign that something is wrong with the system. 

Level and Damping Control Switch

There are both manual and automatic means to adjust the vehicle level. Using a switch near the shift lever, you can raise the vehicle 20-25mm (market dependent). There is a second switch that changes the vehicle's drive modes. These are the three modes discussed above: Comfort, Sport 1, and Sport 2. Sport 1 and Sport 2 lower the vehicle 15mm (market dependent). The suspension is also adaptive and automatically switches the damping profile to Sport 1 above 100 mph.

Compressor and Compressor Relay/Fuse

The compressor provides the system pressure for raising the vehicle as well as a pressure relief valve for lowering it. The compressor relay is responsible for starting and stopping the compressor.

Mercedes-Benz CLS-Class & E-Class Compressor, Relay/Fuse Location

The compressor is located in the forward portion of the front-left wheel well. The compressor relay is located on the left side of the engine compartment, in the relay/fuse box, and is easily identifiable. It is clipped on the rearmost part of the box and is usually black in color. The Airmatic fuse is located in the passenger compartment's right footwell. You must pull back the carpeting and the plate that mounts the suspension control module to access the fuse. The fuse is in position 74.

Level Sensors

The level sensors are mounted on a bracket near the upper control arms on the front of the vehicle. Each sensor is connected to a link rod attached directly to the upper control arm. The sensors produce a voltage that the Airmatic Control Module translates to axle height. A single rear axle level sensor is located near the rear-left drive axle.

Acceleration Sensors

Located at various points in the interior and exterior of the vehicle. The sensors measure turn rate and lateral acceleration. Information from these sensors is used to calculate vertical and horizontal acceleration.

Mercedes-Benz CLS-Class & E-Class Acceleration Sensor Location

The front lateral sensors are located on the strut tower just forward of the front air strut.

Valve Block Assembly

This assembly distributes air to each front strut and the rear axle. It also has a direct connection to the air compressor and has a pressure sensor for the system.

Mercedes-Benz CLS-Class & E-Class Valve Block Location

The valve is easily located as it's positioned directly next to the compressor.

Main Reservoir

The main reservoir is a metal pressure vessel that stores compressed air between 13-16 bar and is used to level the vehicle. This tank is incorporated to reduce the dependency on the air compressor and to reduce noise. The tank is most commonly used to level the car when opening the door or trunk. 

Mercedes-Benz CLS-Class & E-Class Main Reservoir Location

The main reservoir is easy to locate and access. It's located in the right rear corner of the trunk. 

Strut & Damper Assembly

The air strut is an assembly consisting of a monotube shock absorber with electromagnetic damping valves that change settings based on commands from the suspension control module. An air spring assembly sits on top of the strut and is responsible for height adjustment and damping. The air spring contains two chambers: one is used when a firm spring rate is needed, and both chambers are filled for a softer spring rate. 

Air Springs

Located at the vehicle's rear, the air springs consist of an electronically controlled main cell and an additional reservoir. The springs mount to the subframe and lower control arm. If you need to replace them, the subframe must be dropped if factory-style air springs are used. Out of all the components in the system, this is one of the most prone to leaks. If moisture gets in the air spring reservoir, the aluminum corrodes and becomes pitted where it is clamped to the rubber hose, forming an incomplete seal.

Rear Axle Distribution Block

The air system is designed without a direct air line connection between the valve block assembly and the individual rear air springs. Instead, the distribution block splits pressure from a single connection at the valve block to individual lines to each air spring. 

Mercedes-Benz Airmatic System Maintenance/Common Failures

Since this system was introduced nearly twenty years ago, maintenance is becoming a must, and you'll probably want to keep an eye out for its common failures. 

• Air Strut Assembly - ~105,000 Miles
  • The dampers usually still have a little life left in them. However, the air bladders begin to fail around this mileage. You want to listen closely for a hissing noise after the suspension begins to rise. 
• Air Spring - ~115,000 Miles
  • This is the most common failure on Mercedes-Benz equipped with Airmatic. It's common for them to leak from the hose connection at the reservoir and have a bag rupture from age. Solenoids are part of the rear bags, so if one side is lower than the other, suspect a faulty bag.
• Dampers - ~ 115,000 Miles
  • These are simple, and as they age, there will be a noticeable degradation of the ride quality. You might also notice side-to-side body motion that's not controlled as well as pitching and diving. 
• Valve Block - No Mileage
  • The valve blocks in W211/219 are less failure-prone than those in other Mercedes chassis where the solenoids are integrated, such as W220/164. However, if you remove an airline from the valve block and observe aluminum pitting or oxidation, we recommend replacement. 
• Ride Height Sensors - No Mileage
  • The ride height sensor's failures are sporadic. Sensor brackets can be bent or damaged, leading to incorrect or implausible signals. Front links have been known to dry up and pop off.
• Compressor - ~125,000 Miles
  • On a higher mileage vehicle, consider replacing the compressor along with the relay and filter on vehicles that have had multiple bag failures or leaking components for an extended period. These situations tend to overwork the compressor and shorten its life.

Mercedes-Benz Airmatic Suspension Troubleshooting Tips

• Rear Suspension Airbags
   
  • The rear suspension airbags are the most common AIRMATIC failure on the W211. When one side of the rear is lower than the other, this typically is an airbag failure. To determine if one side is lower, raise the vehicle to the highest setting and then lower it. From there, measure the ride height at each corner. Let the car sit overnight with the air suspension computer unplugged, and measure the ride height afterward. If both the initial measurement and the measurement after the car has sat for one day are lower on one side, you can assume that a faulty airbag is the culprit. Unplugging the suspension module will prevent the vehicle from automatically re-leveling overnight. 
    
    When you replace the air spring, you can replace just a single unit with a Genuine or OE component. If you are replacing it with an aftermarket unit, both sides should be replaced simultaneously. This is exceedingly important if you don't have the factory-style scan tool to carry out a level calibration after air spring replacement. This is done to account for the differences in air volume that occur with aftermarket products that omit the additional reservoir. 
• Weak Airmatic Compressor
  • A weak compressor will prevent the vehicle from rising or may cause it to rise slowly. If you have the appropriate scan tool, fault codes for "critical vehicle level" or "recovery time during filling" will be present. A healthy compressor should output a minimum of 10 bar on the scan tool. Output can also be verified using a gauge at the compressor output.
    
    A compressor that doesn't run at all could result from a bad compressor or a lack of voltage to the compressor. It's not uncommon for relays to stick and burn out a compressor. If you see battery voltage at the suspension compressor and it still doesn't run, replace the compressor and its relay. If battery voltage isn't present, replace the relay, fuse, and re-test.
    
    • Arnott-branded compressors sold through us include the compressor relay, which should always be replaced. 
• Failed Front Strut Assembly
  
  • Failed front air struts typically fill and almost immediately start dropping when not operating correctly. An audible hissing at the strut assembly is a good indicator of a front strut failure. If the air strut doesn't rise with the compressor activated, manually fill the strut with pressurized air to confirm that you don't have a compressor issue. These can simply be a weak compressor or an air leak between the compressor and the valve block or the valve block and the strut. 
    • You can manually fill the strut without a factory-style scan tool. To do so, consult this short article on how to do so with a specific plug and a 9-volt battery. 
• Level Sensor Failure
  • If your vehicle is noticeably low but there isn't a red error message on the instrument cluster reading "vehicle level too low", a level sensor (or its linkage) is at fault. This is a common issue after hitting a large object or a large pothole, or if the rear linkage becomes bent. 
• Height Loss Overnight in Cold Climates
  • A certain amount of suspension drop is normal in frigid climates. This is due to thermal contraction and can drop up to 30mm in one day. This is perfectly normal and is within the engineered parameters. 

Specialty Tools Required For Servicing Mercedes-Benz Airmatic Suspension

The Airmatic system on your Mercedes-Benz is user-friendly when servicing it. While none of the tools listed below are strictly required, they are invaluable when diagnosing or servicing the system. 

• Baum Mercedes-Benz Airmatic Suspension Line Socket
  • Clearance at the rear airbags is limited, so having this special socket is useful. In a pinch, a 10mm wrench can work, but this is also useful for reaching the connectors to the valve block as well.
• CTA Mercedes-Benz Air Suspension Tester
  • This is useful if you do not have a scan tool and need to verify sufficient pneumatic output to lift the vehicle. This gauge contains an M8 fitting that can be threaded directly into the compressor outlet port.
• Autel MD808 OBD Scanner
  • This scan tool isn't necessary to perform maintenance, but it's extremely handy. It accurately displays the pneumatic output from the computer. 

If you found this guide helpful, have any questions or comments, or want to see anything added, comment in the field below. This guide will be constantly updated as more information and opportunities to document additional content become available.

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Written by :

Kyle Bascombe

Kyle is the Mercedes Catalog Manager at FCP Euro and has been with the company since 2014.