How to Test an Alternator (Without Guessing)
- satterfieldkamren
- 3 days ago
- 1 min read
Before you replace an alternator or a battery, test the charging system. It takes a multimeter and two minutes.
The test
Engine off: battery should read about 12.4-12.7V. Below 12.2V, charge or replace the battery first, then retest.
Start the engine. Voltage at the battery should jump to about 13.8-14.7V. That's the alternator charging.
Turn on the headlights, blower, and rear defrost. Voltage should stay above about 13.0V. If it sags toward 12V, the alternator can't keep up.
Rev to ~2000 rpm and watch for steady voltage, not wild swings.
Other signs
Battery light on the dash.
Dimming headlights at idle that brighten when you rev.
A whining or grinding noise from the alternator bearing.
Burning-rubber smell from a slipping belt.
Next step
If it fails the test, check the belt and connections before condemning the alternator. Shop parts and tools at https://www.humbl.online
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