Volkswagen Group introduced the mild hybrid (MHEV) versions of its TSI/TFSI engines, e-TSI/e-TEC, between 2019 and 2021. The 48V lithium-ion battery support was applied to various engines within the group, with the most common being the 1.0- and 1.5-liter units:

Volkswagen:

• Golf 1.0-1.5 eTSI
• Passat Variant 1.5 eTSI
• Tiguan 1.5 eTSI

Seat:

• Leon 1.0-1.5 eTSI

Skoda:

• Octavia 1.0-1.5 eTEC

Audi:

• A3 35 TFSI
• Q3 45 TFSI
• Q5 45 TFSI

Cupra:

• Leon 1.5 eTSI
• Formentor 1.5 eTSI
• Terramar 1.5 eTSI

These engines, theoretically aimed at improving performance while reducing emissions, have so far caused significant inconvenience to many users due to chronic alternator/charging system failures.

Let’s first examine how these engines work. The main components of the system are:

• 48V Battery: The energy storage unit that powers the hybrid system. It charges via regenerative braking while the vehicle is in motion.
• Starter-Alternator Unit: An electromechanical device that acts as both a starter motor and an alternator. This belt-driven unit is directly connected to the engine's crankshaft.
• DC/DC Converter: Ensures energy conversion between the 48V system and the vehicle’s conventional 12V electrical systems.

Like all hybrids, this system aims to reduce fuel consumption by providing electric motor assistance during low-speed driving or take-off. It also recovers energy generated during braking.

Where is the Problem?

In the Alternator:

• Mechanical or electrical failures due to overloading of the unit.
• Loosening or breaking of the alternator belt.
• Oxidation or contact issues in the unit's connections.

Consequences of These Failures:

• Both the 48V and 12V systems fail to receive power, causing the vehicle’s electrical system to suddenly shut down.
• The car won’t start or may stop while driving.
• The dashboard displays a "48V supply error" warning.

Costs

 According to factory data, this complex and expensive system, developed to achieve approximately 0.5 liters of fuel saving per 100 km, can experience failures in all VAG models equipped with it. The alternator in question is produced by Valeo, which faced legal issues with Audi due to this problem. In some countries, recalls were issued, and free part replacements were offered. However, in countries like Turkey, vehicles not covered by warranty require alternator unit replacement along with the battery, leading to costs between 100,000 and 150,000 TRY, depending on the make and model.

*More powerful Audis like the 50 TDI and 55 TFSI, which also use a 48V hybrid system, face the same risk.

*In some models, like the Audi A4 45 TFSI, a simpler 12V system is used instead of the 48V one. Their alternators are different and do not function as generators, so they are not affected by this issue.

Sources

• ŞikayetVar
• GolfTutkusu
• DonanımHaber
• SeatCupra
• Audi-Sport
• AudiOwnersClub
• EVClinic