Audi A4 Alternator: Specs, Fitment & Common Faults
A genuinely useful diagnostic technique: touching a broomstick to the alternator housing helps confirm whether a noise genuinely comes from it — plus an alarming account of a replaced battery not fixing the fault, with a voltage test revealing the alternator was undercharging at just 11.5 volts.
Illustration for editorial purposes
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OEM Part Number: 06B903016AC (genuine alternator — confirm via VIN) — aftermarket alternators Bosch 0 986 081 340 / Valeo 439642
| Alternators (aftermarket) | B8: Bosch 0 986 081 340 (140 A, freewheel pulley, 6 ribs, 50 mm, remanufactured exchange, plug ID 166, core charge £94.06, excludes vacuum pump); Valeo 439642 (140 A, freewheel, 6 ribs, 51 mm, new, four-point mounting); Valeo 439775 (150 A, freewheel, 6 ribs, 57 mm, new, four-point mounting); Valeo 440680 (180 A, freewheel, 6 ribs, 57 mm, remanufactured exchange, core deposit £50.24); Hella 8EL 015 630-641 (150 A, freewheel, 6 ribs, 50 mm, new); Hella 8EL 011 713-041 (140 A, freewheel, 6 ribs, 56 mm, new); AS-PL A0576S (150 A, freewheel, 6 ribs, 49.5 mm, new, plug PL_2306); Ridex 4G1139 (180 A, freewheel, 6 ribs, 49 mm, new, LIN2 plug 238, excludes vacuum pump). B9: Lucas LRA03152 (180 A, freewheel, 6 ribs, 49 mm, remanufactured, LIN2A plug, core £25.12, Valeo-built units only) |
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| Outputs & variants | On the B8 four outputs appear: 115 A (AS-PL A3328, a five-rib unit for the early 1.8 TFSI), 140 A for the mainstream petrol engines, 150 A for the 2.0 TDI and most diesels, and 180 A (Valeo 440680, Ridex 4G1139 and 4G1283, AS-PL A0409) for the 3.0 TDI, 3.2 FSI and S4. Both freewheel and rigid pulleys are listed on the B8; the Ridex 4G0121, 4G1002, 4G0966 and 4G1080 are rigid-pulley units. On the B9 the range moves up: 150 A for the 1.4 and 2.0 TFSI, 180 A for the 2.0 and 3.0 TDI and higher-spec petrols, a 210 A Lucas LRC00009 unit, and a 48 V 250 A belt starter-generator (Stardax STX110089R) for the mild-hybrid cars. |
| Genuine (OE) numbers quoted | B8: 0125711130 (AS-PL A0576S), SG14B022 (AS-PL A3131S), 0124525530 (AS-PL A0429S), 0121715176 (AS-PL A0409), TG11C035 (AS-PL A3328). B9: FG18T079 (AS-PL A3308S), 0121715077 (AS-PL A0492), 0125811035 (AS-PL A0607S), F000BL08DF (AS-PL A01256), 0125811178 (AS-PL A01160). |
| Fitment notes | The B8 engines with a vacuum pump driven off the back of the alternator need the pump transferred, as the Bosch and Ridex units are supplied without it; a freewheel pulley should always be replaced like for like, and the B9 mild-hybrid 48 V units are a separate, much more expensive part that cannot be substituted with a 12 V alternator. Remanufactured Bosch, Valeo and Lucas units carry a core charge refunded on return of the old unit. |
Audi A4 Alternator: Often Blamed on the Battery Instead
On the Audi A4, a weak battery and a failing alternator produce almost identical symptoms at first — dim lights, slow starts, a car that won't hold charge — which is exactly why so many people replace the battery, only to be back at the garage a few weeks later with the real culprit untouched.
Audi A4 Alternator: What It Does
The Audi A4's alternator generates electricity while the engine runs, charging the battery and powering the car's electrical systems directly. A healthy alternator means the battery is mostly there for starting the engine and covering brief demand spikes — not for actually running the car's electronics on its own.
Audi A4 Alternator: Watch: Replacing It
B8 petrol; B9 owners see https://www.youtube.com/watch?v=WZEJ6XAsK58 (A4 2.0T B9 2017-2025)
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A Genuinely Useful, Real Diagnostic Technique Worth Knowing — Audi A4 Alternator
If you're trying to confirm whether a noise is genuinely coming from the alternator, this is genuinely worth trying: touching one end of a wooden broomstick or similar rod to the alternator housing itself, with the other end held close to your ear, can help you hear the noise much more clearly and confirm whether it's genuinely originating from the alternator rather than another nearby component. It's also genuinely worth knowing that these engines have used either a 150 amp Bosch unit or a 180 amp Valeo unit depending on the car, visible by checking the markings on the back of the alternator — worth confirming which specific unit you have before sourcing a replacement, since they aren't interchangeable.
It's also genuinely worth knowing a specific clarification if you're replacing the battery on a car fitted with stop-start: using a standard battery not designed for this system can genuinely affect the engine control unit and disable certain functions, worth confirming you're fitting the correct battery type for your specific car rather than a cheaper standard alternative.
Audi A4 Alternator: Warning Signs, DIY Difficulty & Aftermarket Advice
These are the same regardless of make or model — see our full Alternator Guide for symptoms to watch for (plus a genuinely useful two-minute test to confirm it's not the battery instead), confirming the right amperage and fitment against your VIN, and which brands are worth trusting.
More Audi Alternator
The same part, covered across other Audi models.