Turn off the engine and inspect the alternator belt for wear, looseness, or damage
Check the battery terminals for corrosion and tightness
Start the engine and let it idle
Use a multimeter to measure battery voltage with the engine off
Use a multimeter to measure battery voltage with the engine running
Compare the running voltage to the normal charging range
Turn on headlights, blower, and other electrical loads
Measure voltage again with the engine running and accessories on
Listen for squealing, grinding, or whining noises from the alternator
Check for warning lights on the dashboard
Inspect alternator wiring and connectors for damage or looseness
Test the alternator output at the alternator terminal with a multimeter
Perform a load test if available
Replace the alternator if voltage output is low or unstable