Subaru Impreza Alternator: Specs, Fitment & Common Faults
On the Impreza, 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
Opens live listings in a new tab.
OEM Part Number: 23700AA640 (as quoted in catalogue listings — confirm via VIN) — aftermarket alternators Hella 8EL 011 713-191 / AS-PL A6791S
| Alternators (aftermarket) | AS-PL A6791S (150 A, freewheel clutch pulley, 6 ribs, 52.5 mm, new Standard Line, plug PL_1100, OE 104211-4480); AS-PL A5422S (170 A, freewheel, 7 ribs, 55 mm, new Standard Line, plug PL_3308, OE 23700AA640); AS-PL A5392S (150 A, freewheel, 7 ribs, 55 mm, new Standard Line, plug PL_3308, OE A2TX2381A); Rotovis 9091935 (150 A, freewheel, 6 ribs, 52 mm, remanufactured, COM plug); Ridex 4G1423 (150 A, freewheel, 7 ribs, 55 mm, new, plug C/S/L, without vacuum pump); Ridex 4G1343 (170 A, freewheel, 7 ribs, 54.9 mm, new, without vacuum pump); BV PSH 175.517.170.130 (170 A, freewheel, 7 ribs, 55 mm, new +Line Original); Hella 8EL 011 713-191 (100 A, rigid V-ribbed pulley, 5 ribs, 54 mm, new) |
|---|---|
| Outputs & variants | 170 A freewheel 7-rib 55 mm (Subaru 23700AA640) for higher-load and e-Boxer variants; the 150 A 7-rib A2TX2381A pattern carries over from the previous generation |
| Genuine (OE) numbers quoted | 104211-4480 (AS-PL A6791S); 23700AA640 (AS-PL A5422S); A2TX2381A (AS-PL A5392S); 102211-8640 (AS-PL A4042); 54022232 (AS-PL A4041); A2T39091 (AS-PL A5327) |
| Fitment notes | the two Ridex units are new and the Rotovis is a reman exchange, and the Ridex Reman 4G0005R and Stardax units carry £22 to £30 core charges. |
Subaru Impreza Alternator: Often Blamed on the Battery Instead
On the Subaru Impreza, 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.
Subaru Impreza Alternator: What It Does
Running the Subaru Impreza'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 Impreza Alternator: Watch: Replacing It
Generation not stated; FB20 layout is identical across 2012-on Impreza, so usable either way.
Opens live listings in a new tab.
A Genuinely Definitive, Real Diagnostic Technique Worth Knowing — Subaru Impreza 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 Impreza 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.