The Challenge of Legacy ECUs: Fixing Software Fragmentation in Cars

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The automotive industry is fast changing and vehicles are becoming more developed and complex in nature as software is being integrated more and more in vehicle systems (Legacy ECUs). This change has however posed a major challenge, which is the fragmentation of software that is incorporated in vehicles mainly because of the existence of old Electronic Control Units (ECUs) as well as the difficulties involved in updating the old units.

This paper is about obstacles that automotive manufacturers experience when trying to coordinate such fragmented software environments, particularly given the necessity to update ECU on an ongoing basis and the overlaying problem of integrating computer software into cars.

What Are Legacy ECUs?

Electronic Control Units (ECUs) are a very important part of modern vehicles and have the role of controlling different systems in the vehicle including engine management, safety, infotainment etc. In other cars, mostly those produced before extensive use of digital technologies, ECUs were not made in a way to interact with each other to form a cohesive software environment.

The legacy ECUs are often unable to operate with more modern systems and have obsolete software structures, and in many cases, they are hard to upgrade or incorporate into newer vehicle systems. With the shift toward more integrated, connected, and automated vehicles in the automotive industry, the use of these legacy ECUs has become a significant roadblock. Manufacturers have the dilemma of updating or reinstalling these obsolete units without interfering with the performance of the car or the software ecosystem.

The Impact of Software Fragmentation on Car Software Integration

The interaction of old ECUs and the new car software lead to software fragmentation in cars. Also, in contrast to newer cars that approach software control in a more unified and more centralized way, older cars that use heritage ECUs tend to have a more decentralized way of operation with each ECU being a separate unit. Such a decentralization implies that updates to software, fixes of bugs or enhancements cannot be applied uniformly throughout all ECUs within the car.

This fragmentation causes a number of issues in the process of software integration in a car:

Difficulties in Compatibility: Older ECUs might not be compatible with current software and this might lead to unsuccessful communication between units and this may pose potential safety risks or malfunctions in vehicle performance.
Delay on Updates: Legacy ECUs can have to be updated manually or have to be replaced with hardware to support new software, which makes implementing required updates slow.
High Maintenance: The maintenance and upgrading of a multiplicity of legacy ECUs is resource intensive and demands special expertise, tools and a considerable amount of time.

The Challenge of ECU Updates

Among the main problems introduced by the legacy ECUs, the impossibility to upgrade them in a manner that would be compatible with the current vehicle software systems must be mentioned. Although the newer models may be updated via Over-the-Air (OTA) updates, potentially enhancing the performance of the vehicle, correcting bugs as well as introducing new features, legacy ECUs cannot support such updates.

The situation with ECU updates is even more complicated by the fact that the number of ECUs installed in the modern car is enormous. A standard car will contain more than 50 ECUs, which have the role of controlling a different system or function. It is both an administrative and technical challenge to update all of these units (particularly in a legacy system) at once. In other instances, manufacturers might require physically replacing or upgrading ECUs to match the current software standards which can be very expensive and time consuming.

Addressing the Fragmentation Problem: Modern Solutions

Carmakers are in the process of addressing the software fragmentation issue by implementing a number of strategies:

Centralized Control Units: A move towards the application of more centralized control units, including the central gateway or domain controllers, is contributing to fragmentation minimization. The systems will enable easier integration and management of car software and easier updating and coordination of vehicle functions.
Software Platforms and Frameworks: Most manufacturers are moving toward the use of standard software platforms including AUTOSAR (Automotive Open System Architecture) which offer standardized solutions in the development of ECUs and communication. This guarantees higher compatibility and scalability, which contributes to dealing with the fragmentation between various ECUs.
Over-the-Air (OTA) Updates: OTA technology is a technology that has been increasingly adopted by car manufacturers to enable vehicles to encapsulate software updates in real time. This can be used to bridge the legacy ECUs to newer software systems, and avoid the physical interventions required, and make it easier to update them.
Modular and Scalable Architecture: There are manufacturers that are shifting towards modular and scalable architecture and this architecture makes it easier to integrate new technology into the system without affecting the overall system. This method will enable easer migration between the old systems and the new updates, and the effects of fragmenting will be reduced.

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Also see: US Auto Regulations 2025: EV Laws, AI Rules and Car Tech Policy Explained