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Inspect the alternator visually for signs of damage and loose connections. The alternator is a round, metal engine component, rotated by an engine drive belt.
Inspect the battery cable connections. Look for corrosive build-up or poor connection. Having to work harder than normal to deliver electricity to the battery will drain even a brand-new alternator.
Test the alternator's power with a voltmeter. Connect the voltmeter's red (positive) and black (negative) leads to the red and black battery terminals while the engine is off. Crank the engine and check the reading on the voltmeter's screen. If the alternator is healthy, it should show a reading between 13.6 and 14.3 volts. Anything less is an indication that the alternator is weakening.
Listen for noises coming from the alternator while the engine is running. Noises are a sign of possible bad shaft bearing, shorted diodes or mechanical rubbing. Take the alternator to a car-parts store for further testing.
Tips and warnings
- Check the reading on the voltmeter before cranking the Volvo for a measurement of the voltage in the battery. A good battery should have a reading of between 12.5 and 12.8 volts.
- Never disconnect a battery while the engine is running in an attempt to test the alternator. You'll risk electric shock as well as electrical overload to the alternator and other engine systems.
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