Alternator Troubleshooting Tips

There are several areas which alternator troubleshooting tips should cover: the alternator itself, checking for proper operation and impending failures, the amount of draw on the alternator, the cables and size of wires, connectors and corrosion.

A standard combination voltmeter/ohmmeter will be needed. It's an inexpensive tool and one of the most important for diagnosing today's vehicles. It can be purchased at any auto parts store.

Open the hood and inspect the battery for corroded, broken or loose terminals. Replace as necessary before continuing. Connect the voltmeter to the battery terminals by touching the red voltmeter lead to the positive and the black lead to the negative terminal. The correct voltage should be 12.4 or higher. Continue to watch the voltmeter, while a helper starts the vehicle. The voltage should not drop below 10.5 volts. If it does, there is a bad cell in the battery, and the battery must be replaced.

With the engine running, and all accessories off, the voltage should be close to 14.5 volts or slightly higher. Turn the air conditioning on, the stereo and headlights. The voltage now should be no lower than 13.8 volts. If it is lower the voltage regulator needs to be replaced. If the voltage is lower in either case, the alternator should be replaced.

Check the belt for tension. If pressure is placed in between the pulleys, no more than 1 inch of deflection is acceptable.

If the vehicle is equipped with a stereo with a high amperage draw, check the label for the exact amount of continuous draw. Add this figure to 30 amps. If this exceeds 60% of alternator rating the alternator should be replaced with one with a higher output.

Check for loose grounds and wire connectors. These will cause a heavy draw on the system causing the alternator to overheat.

Another alternator troubleshooting tip is noise related. If the alternator has a squealing noise, the bearings are starting to go. If it as a whining noise, the alternator probably has a bad diode trio. These are one way resistors that convert pulsating AC voltage sine wave to a smoother DC current useable by an automobile. When one fails, the voltage and amperage will drop off.

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