BMW 4 Series Alternator: Specs, Fitment & Common Faults
On the 4 Series, a leaking oil filter housing gasket has genuinely been documented as a primary cause of alternator failure on related engines.
Illustration for editorial purposes
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OEM Part Number: 12318578608 (genuine alternator — confirm via VIN) — aftermarket alternators Bosch 1 986 A00 738 / Denso DAN1126
| Alternators (aftermarket) | Bosch 1 986 A00 738 (180 A, freewheel pulley, 6 ribs, 53.7 mm, new, plug ID 125, excludes vacuum pump); Denso DAN1126 (170 A, freewheel, 6 ribs, 49 mm, new); Denso DAN1127 (210 A, freewheel, 6 ribs, 49 mm, new); Denso DAN1135 (210 A, multi-rib pulley, 8 ribs, 49 mm, new); Denso DAN1464 (180 A, multi-rib pulley, 6 ribs, 48 mm, new); Hella 8EL 015 630-481 (180 A, V-ribbed pulley, 6 ribs, 48 mm, new); Hella 8EL 011 713-651 (220 A, freewheel, 6 ribs, 54 mm, new); AS-PL A6342 (210 A, freewheel, 6 ribs, 48 mm, new, plug PL_2306) |
|---|---|
| Outputs & variants | Outputs run from 150 A to 230 A. 150 A and 170 A (AS-PL A6650S, Denso DAN1126) suit the 420i four-cylinder petrol; 180 A covers the 418d, 420d and 425d diesels and the 428i; 210 A units fit the 430d, 435i and 440i six-cylinders, with the eight-rib Denso DAN1135 and AS-PL A6404S for the six-cylinder petrols; 220 A and 230 A (Hella 8EL 011 713-651, AS-PL A3143, Rotovis 9090862) suit the 435d and M4. Freewheel and rigid pulleys both appear, with diameters from 48 mm to 55 mm. |
| Genuine (OE) numbers quoted | 104210-6500 (AS-PL A6404S), FG23S068 (AS-PL A3143), 021080-1150 (AS-PL A6342), 104211-8181 (AS-PL A6650S). |
| Fitment notes | The six-cylinder cars use an eight-rib pulley on some fitments and a six-rib on others, so the rib count and pulley diameter of the old unit should be confirmed; the Bosch and Ridex units are supplied without the vacuum pump, and only the Stardax unit carries a core charge. |
BMW 4 Series Alternator: Often Blamed on the Battery Instead
On the BMW 4 Series, a failing alternator and a simply weak battery share almost the same symptom set at first: dim lights, sluggish starts, charge that won't hold. Mixing the two up is common, which is why plenty of people replace the battery only to find themselves back at the garage shortly after.
BMW 4 Series Alternator: What It Does
The BMW 4 Series's electrical systems and battery charging both depend on the alternator generating electricity whenever the engine runs. If it's healthy, the battery's job shrinks down to starting the engine and handling brief surges in demand, not powering everything else on its own.
BMW 4 Series Alternator: Watch: Replacing It
F32 430i B48 petrol
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A Genuinely Important, BMW-Specific Finding Worth Knowing — BMW 4 Series Alternator
If this alternator has failed, this is genuinely worth checking before fitting a replacement: a leaking oil filter housing gasket has been documented as a primary cause of alternator failure on related BMW engines, since leaking oil can drip directly onto the alternator and cook its internal components.
It's also genuinely worth knowing that when replacing the alternator, it's wise to also change the serpentine belt, tensioner, and idler pulley at the same time, particularly if they're oil-soaked or high-mileage.
BMW 4 Series 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 BMW Alternator
The same part, covered across other BMW models.