SAP S/4HANA Migration for a German Automotive OEM: From Legacy ECC to Cloud-Native ERP

Bavarian Automotive Group AG had been running SAP ECC 6.0 since 2011. Over more than a decade, the system had accumulated over 800 custom Z-programs, three non-standard payment interfaces, and a heavily modified MRP II configuration that reflected production planning logic unique to their mixed-model assembly lines.

The IT leadership team had two realistic options: a brownfield conversion — essentially an in-place upgrade that would preserve existing customizations — or a greenfield reimplementation on the new platform. Both paths had vocal internal advocates. The brownfield camp argued for speed and continuity; the greenfield camp argued that carrying forward twelve years of technical debt would negate the benefits of S/4HANA.

Apex Cloud Consulting was engaged at the point of decision. We conducted a four-week fit-gap analysis across all SAP modules in scope — FI/CO, MM, SD, PP, and QM — benchmarking the client's processes against S/4HANA standard functionality. The conclusion: 73% of the existing customizations addressed gaps that S/4HANA now covered in standard. A greenfield approach would eliminate the majority of the custom code burden while giving the business an opportunity to adopt S/4HANA best practices.

The target architecture was SAP S/4HANA 2023 on Azure, deployed under the RISE with SAP framework. This gave the client a managed private cloud environment with committed SLAs, built-in backups, and a clear commercial path for future S/4HANA updates. Azure's proximity to the client's existing Azure Data Lake and Power BI environment also meant that real-time financial reporting — one of the key business cases — could be implemented without additional middleware.

The migration used a three-system landscape: development, quality assurance, and production, all hosted on Azure Germany West Central to satisfy data residency requirements. Network connectivity back to on-premises manufacturing execution systems was handled via Azure ExpressRoute with a 10 Gbps dedicated circuit, ensuring that production planning data could flow in near real-time between the shop floor and S/4HANA's MRP Live engine.

Data migration was phased: master data (materials, vendors, customers, and cost centers) was migrated and reconciled first, followed by open items (purchase orders, sales orders, open FI postings), with historical transaction data migrated in parallel to a SAP BW/4HANA instance for reporting continuity.

A SAP migration touches every user who has ever opened a transaction. With 3,400 ERP users across four plants and the central finance organization, change management was as critical to the project's success as the technical work.

Apex Cloud Consulting embedded a dedicated change management track from day one. We trained 140 'S/4HANA Champions' — business process owners and team leaders — who received deep-dive training eight weeks before go-live and then served as the first line of support for their colleagues. End-user training was role-based and delivered through a combination of recorded simulations in the client's test system and live sessions facilitated by the Champions.

The hypercare period — the four weeks after go-live — was staffed with a blended team of Apex consultants and client IT personnel available around the clock. In practice, the volume of critical incidents was low: five P1 incidents were raised in the first two weeks, all resolved within four hours. By week three, the hypercare team had reduced to standard business hours.

The production cutover is the highest-risk moment of any ERP migration. For a manufacturing company, the window available for downtime is determined by production schedules, not IT preferences.

The cutover plan was rehearsed twice in full — once six weeks before go-live and once two weeks before — using a clone of the production ECC system. Each rehearsal was timed activity by activity. By the second rehearsal, the team had reduced the critical path from 68 hours to 52 hours, fitting within the agreed weekend window between Friday 22:00 and Monday 02:00.

The actual cutover completed in 49 hours. The ECC system was locked at Friday 22:00; final delta data loads ran overnight; mock reconciliation completed by Saturday afternoon; business sign-off was obtained at Sunday 16:00; and production on S/4HANA started at Sunday 23:00 — three hours ahead of schedule. There were no rollback events.

Twelve months after go-live, the quantified outcomes matched or exceeded the original business case. Batch processing jobs that previously ran overnight now complete in under two hours, enabling production planners to react to demand changes the same day rather than the following morning. The finance team closed their first month-end in S/4HANA in four days — down from ten in ECC — attributable to the real-time reconciliation capability in the Universal Journal.

The total cost of ownership analysis conducted at the 12-month mark showed €2.1M in savings versus the projected cost of maintaining and extending the ECC landscape for another five years. The largest contributors were the elimination of the custom Z-program maintenance burden (€640K over three years), the reduced infrastructure cost of the RISE with SAP model versus the previous on-premises hardware refresh cycle (€890K), and the decommissioning of three legacy integration middlewares that had connected ECC to downstream systems (€570K).

The business is now planning a second phase: an extension of the S/4HANA platform into supplier collaboration via SAP Business Network, and the deployment of SAP Analytics Cloud against the existing BW/4HANA foundation. Both projects are scoped to begin in Q1 2027.