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

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 Forester Alternator reference plate

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.

A genuinely honest, cautionary account worth knowing before fitting a reconditioned unit: documented cases describe a persistent electrical whirring noise beginning immediately after fitting a refurbished alternator, with the noise persisting even after the unit was independently bench-tested as fine and swapped for another unit from the same supplier — suggesting genuine quality control concerns can affect reconditioned alternators specifically.

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.

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 Forester Alternator: Specs, Fitment & Common Faults

OEM Part Number: 23700AB051

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