What is the output of the alternator on a Subaru Legacy?
The alternator output in a Subaru Legacy is typically rated from about 90 to 150 amps, with charging voltage normally around 13.8 to 14.8 volts when the engine is running. The exact figure depends on the model year, trim, and the specific alternator installed.
The question of output varies with year and equipment. Subaru's Legacy lineup spans several generations with different alternator specs, so ownership and maintenance considerations depend on the exact model. Below is a guide to what the output means, how to verify it, and what to expect for common Legacy configurations.
Understanding alternator output in practical terms
The alternator's job is to keep the car's electrical system charged while the engine runs. The "output" is its maximum current capacity under load, not a fixed number. When you start the engine and turn on lights, radio, climate control, etc., the alternator will supply power up to its rating. In Subaru Legacy applications, you'll typically see:
- An amperage rating printed on the alternator housing (for example, 90A, 100A, 120A, or higher in some modern units).
- A charging voltage of about 13.8–14.8 volts when the engine is running and the battery is in use.
Note: The actual current delivered fluctuates with engine speed and electrical demand, and the alternator's regulator controls the output to keep the voltage within spec.
Common ranges by era
To give a sense of how specs have evolved, here are typical ranges found on Subaru Legacy models across generations; exact numbers depend on year and trim. Before listing, researchers and owners should consult the label on the alternator or the service manual for your VIN.
- Early years and older generations (late 1990s to early 2000s): around 90A.
- Mid-era models (mid-2000s to early 2010s): typically 100–120A.
- Recent generations (2015–present): often 120–150A, with some high-output variants approaching 150A.
These ranges reflect OEM specifications and common aftermarket replacements. Always verify with your specific vehicle's label or documentation for an exact figure.
How to verify the alternator's output on your Legacy
Here are practical steps to confirm what your car's alternator is delivering in real-world conditions:
- Check the alternator label. A sticker or stamping on the housing usually lists the amperage (e.g., 90A, 100A, 120A).
- Measure charging voltage with the engine running and all accessories off. A healthy system will read roughly 13.8–14.8 volts on a good battery.
- For precise current output under load, use a clamp-on ammeter around the alternator output cable while the engine runs. Compare the reading to the rated amperage.
- Inspect the belt and electrical connections; slipping belts or corroded terminals can limit actual output even if the alternator is healthy.
Interpreting the results: if voltage is in range but current output is much lower than the rating, there may be a problem with the regulator, wiring, or battery state of charge. If voltage is low (<13.5V) at idle or under load, it suggests the alternator is not charging properly and should be inspected.
Why the exact number matters for a Subaru Legacy
The alternator rating matters for things like battery charging, starting reliability, and how the electrical system handles accessories. For example, heated seats, rear climate features, high-powered audio, and climate control can push demand high enough that a higher-output alternator provides a smoother experience with fewer parasitic drains.
Owners who perform aftermarket installations or use high-powered audio equipment should consider whether their alternator capacity meets the increased demand, possibly opting for higher-output units or dual-battery setups if needed.
Summary
In summary, there is no single universal number for the Subaru Legacy. The output depends on the model year and installed alternator, but most Legacy models operate with alternator ratings between about 90 and 150 amps, delivering around 13.8–14.8 volts when charging. Always verify the exact spec from the alternator label, the owner's manual, or Subaru's service information for your VIN, and test under real-world conditions if you suspect charging issues.
Additional considerations
If you want more detailed information for a specific year and trim, share the model year and engine type (for example, 2.5i 2008, 2013 2.5i, or 2.0XT) and I can give you the precise OEM spec and recommended diagnostic steps.
How to tell if a Subaru alternator is bad?
How to Know If You're Subaru Alternator Is Failing
- Dim Lights.
- Dead Battery.
- Whirring and Buzzing Noises from the Engine.
- Unusual Electrical Bugs.
- The Car Stalls.
Is 13V good for an alternator?
13+ is good, once driving you'll probably see over 14 volts. Alternators are smart these days and don't need to produce 14+ volts when both batteries are fully charged. Usually see 13 when the battery is charged and 14 when it is being charged like right after you start it.
What is normal alternator voltage output?
A car alternator should put out between 13.5 and 14.5 volts while the engine is running to charge the battery, though the exact voltage can fluctuate with electrical load and engine speed. A steady reading, even with accessories like lights and the radio on, indicates it's working correctly. Readings consistently below 13 volts or above 15 volts can signal a problem.
Normal operating voltage
- Engine running (low load): Approximately 13.5 to 14.5 volts.
- Engine running (high load): The voltage may drop to around 13 volts, but should remain above that while the alternator is functioning correctly.
- Optimal range: Many sources cite a "sweet spot" of around 14.2 to 14.4 volts.
When to be concerned
- Voltage is consistently below 13 volts: This indicates the alternator isn't charging the battery properly, and the battery may be draining.
- Voltage is consistently above 15 volts: This can mean the voltage regulator is failing and overcharging the battery, which can cause damage.
How to test
- Start your car and turn off all accessories like lights, radio, and the heater.
- Place the positive and negative probes of a multimeter on the battery terminals.
- Read the voltage. It should be between 13.5 and 14.5 volts.
- Turn on all accessories (headlights, heater, wipers, radio).
- Check the voltage again. It may drop slightly but should still be at least 13 volts.
Is 14.7 V too high for an alternator?
14.7 volts is at the high end of the normal charging range for an alternator and could be acceptable, but it's borderline and may indicate a developing issue with the voltage regulator. A healthy system typically operates between 13.813.813.8 and 14.514.514.5 volts, but some sources state that up to 14.714.714.7 is normal. If the voltage fluctuates or consistently exceeds 14.814.814.8 volts, it could damage the battery over time.
This video explains how to test your car alternator: 56s1A Auto: Repair Tips & Secrets Only Mechanics KnowYouTube · May 11, 2020
What to do about 14.714.714.7 volts
- Monitor the voltage: Check if the reading is stable or if it increases beyond 14.814.814.8 volts with the engine running. If it consistently stays at 14.714.714.7 volts, it may be a normal variation for your vehicle, especially under heavy electrical load.
- Check other components: Inspect the battery terminals for corrosion or looseness and ensure the alternator belt is not slipping.
- Consult a professional: If the voltage goes above 14.814.814.8 volts or if you have other symptoms like dimming lights or a warning light on the dashboard, have a mechanic check the charging system. A faulty voltage regulator is a common cause for overcharging and requires professional attention.
- Consider replacement: If the voltage is consistently too high, a mechanic will likely need to replace the voltage regulator, which is often part of the alternator itself.
