1990 Mercedes-Benz 420SEL Active Suspension System Diagnosis & Testing Cost

There is no trend regarding active suspension component failure, though age will play a factor with air springs. It is most important to understand that proper maintenance and inspections of the system will catch most concerns before they turn into problems.

The diagnostic strategy for the active suspension system will vary with the issue presented to the technician. For instance, if one air spring fails to inflate, the technician would likely begin by checking the hardware at that air spring or inspecting for leaks. However, if one air spring at a time randomly failed to inflate, the technician would likely begin inspection at the control module. It is less important to understand the diagnostic process for active suspension systems than it is to understand that the process differs greatly depending on the fault exhibited and other clues which may be present. Since modern vehicles use sensors from the engine and transmission control system to adapt to driver inputs, it is also important to note that diagnosing suspension system faults is secondary to diagnosing any other driveability concerns, check engine or transmission warning lights, and anything else that could affect the operation of the active suspension system.

Any time the air suspension system is opened, it should be purged of air before reclosing the system. This will help rid the system of moisture caused by humidity and condensation. Also, this will allow the technician to monitor for debris, and take action if needed.

When diagnosing any active suspension system, the suspension must be deactivated before raising the vehicle with a jack. When the vehicle is lifted, the active suspension will attempt to level itself if left on, and this may result in damage to the active suspension system, or unstable lifting with the jack. If deactivating the system is not possible, disable the compressor.

Diagnosing active suspension systems is nearly always outside of the scope of the DIY mechanic. This is typically due to two factors, availability of high quality and high functioning scan tools, and inexperience servicing computerized automotive systems. The cause of the issue may not be immediately understood as part of the system, and this can lead to misdiagnosis of correctly functioning components due to the inability to detect the real issue. If the fault is not abundantly clear, leave diagnosis of the active suspension system to a trained professional. This will ensure the issue is diagnosed and repaired properly.