The new Audis with 48V mild hybrid technology (A6, A7, A8, Q5, Q7, Q8, and other recent models) use a special 48-volt alternator , also called BAS (Belt Alternator Starter). This system, more advanced than a traditional alternator, is essential for energy recovery and for supporting the engine during starting and acceleration.
In this guide, find out how to replace the 48V alternator on Audi Mild Hybrids safely and without errors.
🔧 WHAT IS THE 48V (BAS) AUDI ALTERNATOR?
The BAS (Belt Alternator Starter) is an integrated starter-alternator , connected by a belt to the internal combustion engine and the 48-volt electrical network . It has several functions:
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Generates energy while driving.
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Supports the engine when starting (start-stop function).
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Recovers energy during braking (regeneration).
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It helps in the acceleration phase.
Unlike classic 12V alternators, it is connected to a 48V lithium-ion battery and constantly communicates with the engine control unit (ECU).
Read Also: WHAT IS THE 48V BAS AUDI ALTERNATOR?
⚠️ WARNINGS BEFORE PROCEEDING
WARNING : The 48V system is dangerous!
It should never be treated as a simple 12V system. Follow all precautions required by VDE regulations .
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ALWAYS disconnect the batteries (both 12V and 48V) before starting.
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Wear certified insulating gloves .
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Wait at least 10 minutes after disconnecting to avoid residual discharges.
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The use of official diagnostic tools such as ODIS or VCDS is essential.
🛠 PROCEDURE TO REPLACE THE 48V ALTERNATOR ON AUDI
The procedure may vary slightly depending on the model and engine, but the basic steps are as follows:
1. Vehicle preparation
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Park the vehicle on a level surface and apply the handbrake.
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Disconnect the 12V battery first, then the 48V battery.
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Remove any engine covers or underguards.
2. Access to the BAS
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The BAS is located in the lower front part of the engine, connected by a belt.
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You may need to:
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Remove the front bumper .
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Remove the front crossmember .
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Raise the engine slightly to create space.
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3. Removing the 48V alternator
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Loosen the automatic tensioner and remove the service belt .
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Carefully disconnect the BAS (high voltage) connector .
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Remove the fixing bolts (usually 3 or 4).
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Remove the alternator from the engine compartment.
4. Installing the new BAS
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Insert the new 48V alternator.
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Tighten the bolts to the specific torque recommended by the manufacturer.
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Reconnect the electrical connector , checking for corrosion.
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Reinstall the service belt.
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Reassemble the removed protections.
5. Recovery and diagnosis
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Connect the 12V battery first, then the 48V.
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Perform an adaptation with ODIS or VCDS to recognize the new component.
Read Also: WHAT IS MEANT BY ADAPTATION WITH ODIS OR VCDS?
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Clear any DTC errors and verify correct operation.
Read Also: What are Diagnostic Test Codes (DTC)? Their Meaning, Structure, and How to Interpret Them
📌 AUDI MODELS THAT USE THE 48V MHEV SYSTEM
The 48V mild hybrid system is present on many Audis produced from 2018 onwards. Here are the most common models:
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Audi A6 (C8)
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Audi A7 Sportback
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Audi A8 (D5)
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Audi Q5, Q7, Q8
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Audi S6, S7, S8 with TDI engines
Always check your vehicle's VIN or consult your Audi workshop manual to ensure compatibility.
❓FREQUENTLY ASKED QUESTIONS (FAQ)
▶ Where is the 48V alternator located on new Audis?
Usually in the lower front part of the engine, passenger side.
▶ Can I replace the BAS on an Audi Mild Hybrid myself?
Only if you're a professional or trained mechanic. The 48V system is dangerous for the inexperienced.
▶ Is diagnosis necessary after replacement?
Yes, a diagnosis with VAG equipment is required to recognize the new alternator and clear the errors.
▶ How much does a 48V Audi alternator cost?
The average price varies between €600 and €1,200 for the component alone, plus labor.
🔍 CONCLUSIONS
Replacing the 48V alternator on new Audis is no easy task. It requires care, expertise, and the right tools to avoid damage and danger. If you're a mechanic or run a workshop, invest in training and equipment to work safely with 48V systems. If you're a private individual, consult a qualified professional.
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