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

OEM Part Number: 23700AB051

Accuracy note: genuine reference varies by generation — current generation shares one reference across Legacy, Outback, Forester, WRX, Crosstrek, and Impreza.

Current generation (shared reference)	Subaru OEM: 23700AB051
1999-2002 era, shared reference	Subaru OEM: 23700AA390

Often Blamed on the Battery Instead

A weak battery and a failing alternator produce almost identical symptoms at first — dim lights, slow starts, a car that won't hold charge — which is exactly why so many people replace the battery, only to be back at the garage a few weeks later with the real culprit untouched.

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.

What It Does

The alternator generates electricity while the engine runs, charging the battery and powering the car's electrical systems directly. A healthy alternator means the battery is mostly there for starting the engine and covering brief demand spikes — not for actually running the car's electronics on its own.

Subaru Outback Alternator reference plate

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.

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.

Subaru Outback Alternator: Specs, Fitment & Common Faults

OEM Part Number: 23700AB051

Shop for This Part on eBay

A Genuinely Definitive, Real Diagnostic Technique Worth Knowing — Subaru Outback Alternator