Subaru Outback Alternator: Specs, Fitment & Common Faults

A genuinely definitive diagnostic technique: removing the alternator belt and starting the engine confirms or rules out the alternator entirely — plus a cautionary account of a reconditioned alternator causing its own persistent noise.

Illustration for editorial purposes

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OEM Part Number: 23700AA401 (as quoted in catalogue listings — confirm via VIN) — aftermarket alternators Bosch 1 986 A01 427 / Hella 8EL 011 713-191

Accuracy note: Covers the Subaru Outback (BS 2015-2020) as listed in the UK aftermarket catalogues. Alternators are sold by output (amps), pulley type and plug, and the same model usually has two or three units depending on engine, start-stop and the electrical load of the trim — a 120 A unit on a car built for 150 A will undercharge, and a rigid pulley on a car designed for a freewheel clutch pulley will shred belts. The references below are UK aftermarket catalogue listings for this generation, labelled by brand; many are remanufactured exchange units that carry a core charge until the old alternator is returned. Genuine numbers are shown only where a listing quotes one. Check the amp rating, pulley and plug stamped on the old unit, or confirm via VIN, before ordering.

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 A5659S (130 A, freewheel, 6 ribs, 52.5 mm, new Standard Line, plug PL_1100, OE A5TV0081A); AS-PL A5486S (130 A, freewheel, 6 ribs, 52.5 mm, new Standard Line, plug PL_1100, OE A5TV0881); AS-PL A5359 (130 A, freewheel, 6 ribs, 52.5 mm, new Standard Line, plug PL_3308, OE A2TX3382AC); AS-PL A5392S (150 A, freewheel, 7 ribs, 55 mm, new Standard Line, plug PL_3308, OE A2TX2381A); Rotovis 9091933 (130 A, freewheel, 6 ribs, 52 mm, remanufactured, COM plug); Ridex 4G1343 (170 A, freewheel, 7 ribs, 54.9 mm, new, without vacuum pump); Ridex 4G1423 (150 A, freewheel, 7 ribs, 55 mm, new, plug C/S/L, without vacuum pump)
Outputs & variants	150 A and 170 A freewheel 7-rib 55 mm for the 2.0 D diesel and the 2.0 DIT turbo
Genuine (OE) numbers quoted	A5TV0081A (AS-PL A5659S); A5TV0881 (AS-PL A5486S); A2TX3382AC (AS-PL A5359); 23700AA401 (AS-PL A5425S); A2TX2381A (AS-PL A5392S)
Fitment notes	Three different 130 A Mitsubishi numbers appear for the same output, so quote the number on the old unit when ordering; Stardax, Walker, DRI and Autoelectro are exchange-style units with core charges from £22 to £125 refunded on return of the old alternator.

Subaru Outback Alternator: Often Blamed on the Battery Instead

On the Subaru Outback, it's genuinely hard to tell a weak battery from a failing alternator just from symptoms — both produce dim lights, slow starts, and a battery that won't hold charge. That's exactly why so many people end up replacing the wrong part, then returning to the garage a few weeks later.

Before you buy: alternator output rating varies by engine size and trim, particularly on cars with more onboard electronics. Always confirm against your VIN before ordering.

Subaru Outback Alternator: What It Does

Running the Subaru Outback's electrical systems and keeping the battery charged while the engine turns over — that's the alternator's role. A properly functioning one means the battery only really needs to worry about starting the car and absorbing occasional spikes in demand.

Subaru Outback Alternator: Watch: Replacing It

🎬 Watch: How to Replace Alternator 2015-2019 Subaru Outback

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BS 2.5

Subaru Outback Alternator reference plate

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A Genuinely Definitive, Real Diagnostic Technique Worth Knowing — Subaru Outback 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. If the noise persists with the belt off, the alternator is ruled out entirely and the cause lies elsewhere in the accessory belt system; if it disappears, you've confirmed the alternator or its own pulley bearing as the genuine source.

A genuinely honest, cautionary account worth knowing before fitting a reconditioned unit: one documented case saw a persistent electrical whirring noise begin immediately after fitting a refurbished alternator, with the noise persisting even after the unit was independently bench-tested as fine and then swapped for another unit from the same supplier — suggesting genuine quality control concerns can affect reconditioned alternators specifically. If a new noise begins right after fitting a reman or refurbished unit, it's worth considering the replacement part itself as a genuine possible cause, rather than assuming the noise must be coming from somewhere else on the car.

It's also genuinely worth knowing that on H6-equipped models, the alternator differs from the four-cylinder H4 versions, and some noise specifically under a genuinely heavy electrical load has been described by at least one professional rebuilder 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 Outback 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.