BMW 2 Series Alternator: Specs, Fitment & Common Faults
On the 2 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 DAN1464 (180 A, multi-rib pulley, 6 ribs, 48 mm, new); Denso DAN1135 (210 A, multi-rib pulley, 8 ribs, 49 mm, new); Hella 8EL 015 630-491 (150 A, V-ribbed 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 units (Hella 8EL 015 630-491, Denso DAN1126) suit the 218i and 220i four-cylinder petrols; 180 A units cover the 218d, 220d and 225d diesels and the 228i; 210 A eight-rib units (Denso DAN1135, Ridex 4G1143, AS-PL A6404S) fit the six-cylinder M235i and M240i; 220 A and 230 A units (Hella 8EL 011 713-651, AS-PL A3457S, Rotovis 9090862) suit the M2 and high-load six-cylinders. Pulley rib count is the quickest check, as the six-cylinder cars use an eight-rib pulley. |
| Genuine (OE) numbers quoted | 104211-8181 (AS-PL A6650S), 021080-1150 (AS-PL A6342), 104210-6500 (AS-PL A6404S), FG23S033 (AS-PL A3457S). |
| Fitment notes | Both Bosch/SEG and Denso/Valeo type alternators were fitted, with pulley diameters from 48 mm to 55 mm and mixed freewheel and rigid pulleys, so the old unit must be matched by rib count and pulley diameter; the Bosch and Ridex units are supplied without the vacuum pump, and only the Stardax unit carries a core charge. |
BMW 2 Series Alternator: Often Blamed on the Battery Instead
Because a weak BMW 2 Series battery and a dying alternator both cause dim lights, slow starts and charge that won't hold, it's an easy mistake to replace the wrong one first. That mix-up sends plenty of people back to the garage a few weeks later, the real fault still there.
BMW 2 Series Alternator: What It Does
Every time the BMW 2 Series's engine runs, the alternator is generating the electricity that charges the battery and directly feeds the electrical systems. A properly working alternator leaves the battery mostly responsible for engine starts and short demand spikes — not for running the electronics unaided.
BMW 2 Series Alternator: Watch: Replacing It
F22 228i N20; same job on 220i
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A Genuinely Important, BMW-Specific Finding Worth Knowing — BMW 2 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 2 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.