Subaru Forester Alternator: Specs, Fitment & Common Faults
On the Forester, removing the alternator belt and starting the engine genuinely confirms or rules out the alternator entirely as the source of a noise.
Illustration for editorial purposes
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OEM Part Number: 23700AB051 (genuine alternator — confirm via VIN) — aftermarket alternators Bosch 1 986 A01 427 / AS-PL A5392S
| Alternators (aftermarket) | Bosch 1 986 A01 427 (130 A, freewheel clutch pulley, 6 ribs, 52.5 mm, new, plug 163, without vacuum pump, £7.31 core charge); AS-PL A5392S (150 A, freewheel, 7 ribs, 55 mm, new Standard Line, plug PL_3308, OE A2TX2381A); AS-PL A5349 (170 A, freewheel, 7 ribs, 55 mm, new Standard Line, plug PL_3308, OE A3TX0781); AS-PL A5518S (130 A, rigid pulley, 6 ribs, 55 mm, new Standard Line, plug PL_3308, OE A2TX3291); AS-PL A5359 (130 A, freewheel, 6 ribs, 52.5 mm, new Standard Line, plug PL_3308, OE A2TX3382AC); AS-PL A5126 (110 A, rigid pulley, 6 ribs, 55 mm, new Premium Line Mitsubishi-sourced, plug PL_3308, OE A2TL0291); Ridex 4G1423 (150 A, freewheel, 7 ribs, 55 mm, new, plug C/S/L, without vacuum pump); Rotovis 9091925 (150 A, freewheel, 7 ribs, 55 mm, remanufactured, plug C/S/L) |
|---|---|
| Outputs & variants | 130 A in two forms, a rigid 6-rib 55 mm (A2TX3291) and a freewheel 6-rib 52.5 mm (A2TX3382AC / Bosch 1 986 A01 427); 150 A and 170 A freewheel 7-rib 55 mm (A2TX2381A / A3TX0781) for the 2.0 XT turbo and 2.0 D diesel |
| Genuine (OE) numbers quoted | A2TX2381A (AS-PL A5392S); A3TX0781 (AS-PL A5349); A2TX3291 (AS-PL A5518S); A2TX3382AC (AS-PL A5359); A2TL0291 (AS-PL A5126); 439866 (AS-PL A3719) |
| Fitment notes | the freewheel and rigid 130 A units are not interchangeable because the pulley diameter differs, and the Walker, DRI and Autoelectro exchange units carry core charges of £45 to £125 refunded when the old unit is returned. |
Subaru Forester Alternator: Often Blamed on the Battery Instead
Because a weak Subaru Forester 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.
Subaru Forester Alternator: What It Does
Every time the Subaru Forester'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.
Subaru Forester Alternator: Watch: Replacing It
Covers FB-engine Forester; 2009-13 SH version at jWWzAvrGnbQ if SJ-specific needed
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A Genuinely Definitive, Real Diagnostic Technique Worth Knowing — Subaru Forester Alternator
If you're chasing a whine or squeal that might be coming from the alternator, the power steering pump, or a belt tensioner, this is genuinely worth knowing: removing the alternator's drive belt entirely and briefly starting the engine to see whether the noise disappears is a genuinely definitive way to confirm or rule out the alternator itself, since with the belt removed the alternator physically cannot be spinning or making noise.
It's also genuinely worth knowing that some noise specifically under a genuinely heavy electrical load has been described as difficult to reproduce except under loads well beyond what the car would typically draw at idle — worth bearing in mind that not every noise heard only under heavy load necessarily indicates a fault.
Subaru Forester 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 Subaru Alternator
The same part, covered across other Subaru models.