Electric Vehicle Parts Information

Repair of the Starter/Generator on an Audi A6

Problem Background
The 48V starter-generators in Volkswagen Group vehicles manufactured after 2018, equipped with the Mild Hybrid (MHEV) system, have earned a somewhat notorious reputation. The issue has even led to multiple recall campaigns and the term “mild hybrid disaster” in Western automotive media. The root cause is relatively straightforward: the system was new to the brand, and engineers miscalculated the required parameters. When functioning as a generator, the device would produce excessive current.

This resulted in overheating of the power transistors and failure of the generator's power board. The problems then cascaded: the disabled generator caused the 48V battery to fully discharge, and subsequently, it entered a locked state. This required not only repairs to the starter-generator but also unlocking the battery using Audi’s proprietary ODIS software.

This problem has been well-documented, and today, it can be resolved through reprogramming the starter-generator and replacing the power boards when necessary. However, is the fault always with this component? Sometimes, extra care during installation is crucial. In modern vehicles, nothing is insignificant—especially not seemingly minor details like coolant and its pump.

Repair History
We received a 2018 Audi A6 diesel equipped with the MHEV system. The client had recently purchased a starter-generator from us to replace the previous one, which had burned out. However, the installation was done independently. By the time the vehicle was brought to us, the new generator had already stopped functioning, the 48V battery was discharged, and it was locked.

Diagnostic Results
In addition to the standard errors from the control module related to the starter-generator and hybrid drive battery, there was also a critical temperature reading of -50°C, indicating a lack of coolant. Moreover, we found that the client had failed to update the firmware via ODIS after installing the new generator, which is a serious violation of the installation protocol.

This was not the only oversight. Since the 48V starter-generator uses liquid cooling, it is necessary to properly fill the cooling system after installation—removing air pockets and topping up the coolant to the appropriate level. The client skipped this step, leading to the third and most serious installation error.

Our diagnostics revealed that the root cause of the problem was not the generator itself but a seized electric pump. The faulty water pump prevented proper circulation in the cooling system, leading to inadequate cooling of the equipment.

Work Performed

• Replaced the generator, as the one previously sold could not be repaired—it had burned out.
• Reprogrammed the new generator with updated firmware and correctly commissioned it.
• Replaced the seized electric water pump.
• Cleared the critical error on the battery to allow it to accept a charge.

Advice and Warnings
This case clearly demonstrates the importance of consulting professionals with the necessary experience and expertise, especially in highly specialized fields, when repairing modern vehicles.

It also highlights the need to pay attention to all details and nuances and strictly adhere to the prescribed procedures during repairs.