To properly test an alternator, the battery must be in good condition. It should have a full charge and no dead or shorted cells. Honda Civic alternators are rated for a maximum of amperage output, although this total output rating is only a flash rating. This means that the alternator can provide this amperage for a very short period. The amperage depends on the year of the Honda Civic. The alternator heats up rapidly at this maximum amperage output and will destroy itself if required to maintain this output. An alternator should run at no more than 30 to 40 per cent of maximum output.
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Check the tension on the drive belt and make sure that it is tight enough so that the alternator is not slipping.
Turn the voltmeter to the 20-volt scale and probe the positive and negative terminals on the battery. The voltage should be 12.5 to 12.7 volts. If not, charge the battery.
Check the battery for voltage drop as the vehicle is started. The voltage should not drop below 10.5 volts. If it drops below 10.5 volts, the battery has a bad cell and needs to be replaced.
Check the voltage at the battery with the engine idling and look for 14.5 volts plus or minus .8 volts. Turn on the headlights and the air conditioning and watch the voltmeter to make sure the voltage does not drop below 13.8 volts. If the voltage observed was less than these parameters, one or more of the diode banks are bad and the alternator needs to be replaced.