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 Numbers
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.
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.
Fitment & Compatibility
Alternator output rating differs between engine sizes and trims of the Forester, with higher-spec cars carrying more onboard electronics that demand a higher-output unit. Always confirm the exact part number for your specific engine before ordering. Whether you're sourcing a replacement alternator for your Subaru Forester from a dealer, specialist, or online marketplace, always check compatibility against your registration or VIN before buying.
Common Faults
Symptoms of Failure
- Dashboard battery warning light — the most direct signal, though it can also indicate a battery or wiring fault rather than the alternator itself.
- Dimming or flickering headlights — especially noticeable at idle or low revs, when the alternator struggles most to keep up with demand.
- Whining or grinding noise from the engine bay — can point to a worn bearing inside the alternator itself.
- Battery repeatedly going flat — if a new battery keeps discharging, the alternator is often the real cause rather than the battery being faulty again.
DIY Replacement Difficulty
This is a moderate DIY job on most versions, though access varies significantly depending on engine layout — some require removing other components to reach the alternator, which can extend the job considerably. Expect 1–3 hours for an experienced home mechanic depending on access, or around an hour of labour at a garage with the right tools.
A Genuinely Definitive, Real Diagnostic Technique Worth Knowing
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.
OEM vs. Aftermarket
Reputable aftermarket alternators are generally a safe, cost-effective alternative to OEM parts, provided they match the correct output rating for your specific trim. Remanufactured units from established brands are also a solid middle-ground option, often coming with a warranty comparable to new parts at a lower price.
More Subaru Alternator Guides
The same part, covered across other Subaru models.