BMW 740Ld xDrive Active Suspension System Control Module Replacement Cost

Active suspension systems on modern vehicles use hydraulic or pneumatic pressure to change the ride height, dampening characteristics, and rigidity of the suspension according the the road surface any precise moment. They will typically use a pump or compressor to send pressurized fluid or air to the suspension on each corner of the vehicle, which will raise or lower the vehicle, or increase and decrease stiffness. In order to control this action, a central computer, the active suspension system control module, will use feedback from pressure sensors, yaw sensors, and ride height sensors to determine when and how the vehicle should react.

The active suspension system control module functions by comparing sensor readings from each corner of the vehicle, speed, throttle application, and a variety of other vehicle sensor readings to determine the best possible position for the suspension is for that moment, and use the compressed air or pressurized fluid to make adjustments. The result is a vehicle that stays level when parked, rolls less during turns, and conforms to the road manners the driver desires. Like other control modules and control units, the active suspension system control module is a small computer which is capable of referencing preset data very quickly during vehicle operation.

Since the active suspension system control module is the brain of the entire system, it can mimic the issues of any one part of the system, or show multiple signs of failure. Symptoms can, but not necessarily, include a service warning light for the suspension, ABS or traction control systems, unexpected suspension adjustments, extreme raising or lowering of the vehicle, or lack of adjustability. These symptoms can exhibit themselves at one or more corners of the vehicle, and may be intermittent or permanent.

The urgency of the repair is based on the type and severity of the issues resulting from failure of the control module for the suspension system. If the ABS and traction control systems are turned off, the vehicle should be repaired immediately since these are safety systems that the driver is likely accustomed to using. When the symptoms have a noticeable effect on handling and driveability, again, this should be repaired before the situation turns hazardous. However, if the suspension system gives no reason for handling, drivability, or safety concerns, the repair can likely wait until the earliest convenience.

Control modules and other electronics of all kinds fail, but there is no clear pattern of failure for active suspension system control modules. If the control module is to fail for any vehicle, it will likely show no connection with other similar vehicles pertaining to age or mileage at the time of failure. In general, ensuring that the charging system for the vehicle is maintained properly should help the electrical and computerized systems on the vehicle function more accurately and for a longer duration.

The diagnostic strategy for the active suspension system control module 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.

Once the control module has been recognized as the failed component, the technician will remove any obstructing covers or trim components, inspect and ensure the wiring harness and connectors for the module are in working order, and remove mounting hardware to remove the control module. Once the new control module is in place, the trim or other obstructions can be replaced and programming of the module can begin. As with most other procedures for automotive repair, the system will be tested before returning it to the customer.

We recommend thorough testing of the active suspension system before replacing any parts that are suspected of failure. Since the control module uses the inputs of the various sensors around the vehicle to perform its functions, it can easily mimic the failure of those electrical sensors and components. This has led to the costly replacements of good components on many occasions.

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 and replacing the control module for many systems is 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. As stated before, the control module can mimic issues that any component of the system can cause, and the cause of the issue may not be immediately understood as part of the system. 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.