alternator / dynamo Audi RS6 (C8) 4N0.903.028.R 51km

Part Number: 4N0.903.028.R (4N0903028R)

Manufacturer: Continental / Vitesco Technologies

Mileage: 51 km (Delivery Mileage / Virtually New)

System: 48V Mild Hybrid Electric Vehicle (MHEV)

The 4N0.903.028.R is not a traditional alternator; it is a Belt Starter Generator (BSG). In the 2020–2024 Audi RS6 (C8), this unit is the heart of the 48V mild hybrid system. It replaces the conventional starter motor for warm starts and acts as a high-output generator capable of recuperating up to 12 kW of power during deceleration.

Technical Specifications

• Voltage: 48V (Integrated into the vehicle’s high-power electrical sub-grid).

• Cooling: Liquid-cooled (Connected to the engine’s low-temperature coolant circuit).

• Drive: Heavy-duty ribbed V-belt with a specialized tensioner system to handle bi-directional torque.

• Recuperation Power: Up to $12\text{ kW}$ sent directly to the lithium-ion battery in the trunk.

• Boost Function: Can provide a small amount of torque assist to the $4.0\text{ TFSI}$ V8 engine during initial take-off to smooth out turbo lag.

Key Features of the “R” Revision

• Reliability Update: The “R” suffix is one of the most recent hardware revisions. Earlier versions (such as the “H” and “J” suffixes) were subject to a major global recall due to internal moisture ingress causing electrical shorts. The “R” revision features upgraded internal sealing and revised control electronics.

• Silent Start: Enables the “sailing” or “coasting” function where the V8 engine shuts off completely at speeds between $55\text{–}160\text{ km/h}$; the BSG restarts the engine instantly and imperceptibly when the driver touches the throttle.

• 51 km Condition: At this mileage, the internal bearings, carbon brushes (if applicable), and the liquid-cooling seals are in factory-perfect condition.

Professional Installation & Critical Notes

1. Software Management (SVM): After installation, the new BSG must be “learned” by the Gateway and Battery Management Controller. This requires Audi ODIS to perform a Software Version Management (SVM) update to ensure the 48V battery charging parameters are synced.

2. Cooling System Bleeding: Since this unit is liquid-cooled, the coolant circuit must be bled using a vacuum tool. Air pockets inside the BSG housing will lead to rapid overheating and internal electronic failure.

3. Belt Replacement: Audi recommends replacing the specialized 48V drive belt whenever the BSG is removed. This belt is under significantly higher tension than a standard 12V alternator belt.

4. 48V Safety: While not as dangerous as a full EV battery, the 48V system can still cause significant arcing. Ensure the 48V battery in the luggage compartment is disconnected (and the 12V battery) before beginning work.

Inventory Tip: This part is a high-demand “safety-critical” component. Owners of 2019-2021 RS6/RS7 models often seek the “R” revision as a preventative upgrade to avoid the well-documented 48V charging system failures.