Automotive Charging System Problems

by David Eiranova

The charging system of a car is one system that can really make it obvious when there's a problem. An automotive charging system is responsible for supplying current to the car's circuits and for keeping the battery at full charge. Read on to discover the fundamental parts of the automotive charging system, as well as the various problems that can occur and the symptoms that accompany such problems.

Charging system fundamentals

There are six major parts to an automotive charging system. They include the alternator, the voltage regulator, the alternator drive belt, the charge indicator, the charge system wiring harness and the battery. The alternator drive belt transfers power from the engine to drive the alternator, which is an AC generator. After the engine starts, the alternator supplies all the current used by the car and keeps the battery at full charge. Problems with any of these components will show up in various ways.

Symptoms of automotive charging system problems

Four common symptoms of problems with the charging system include a dead battery, an overcharged battery, grinding, buzzing or squealing noises, and a charging system indicator lamp on all the time. Some of these symptoms can be caused by faults in other systems, such as a bad starter, computer failure, or a defective battery, so diagnosis may be tricky.

Automotive charging system problems

A visual inspection of the parts of the charging system will often reveal the cause of the problem, such as a loose or missing drive belt, corroded battery cables or terminals, or wiring problems. Other problems, such as a problem with the voltage regulator, Electronic Control Module or a bad alternator will take further diagnostic tests to discover. Common tests include a charging system output test, a regulator voltage test, a regulator bypass test and a circuit resistance test. These tests are performed with a load tester or a VOM (volt-ohm-milliammeter). Sometimes an oscilloscope can be used to pinpoint the problem.

Test procedures

To use a load tester for a charging system output test, fasten the two leads to the battery and clip the inductive amp pickup around the insulation on the negative battery cable. Turn the ignition key switch to "run" and record the ammeter reading. Start the engine and let it idle. Adjust the load control on the tester until the ammeter shows the current output (do not let the voltage drop below 12 volts). Adding the two ammeter readings will show the total charging system output in amps, which should be compared against the rating of the alternator. This test is the most commonly used to determine if there is a problem with the charging system. The other tests mentioned in the previous section may be used to pinpoint the problem if the charging system output current is found to be low.


Disconnect the battery before removing any component of the charging system. Failure to do so may result in damage to sensitive electronic components. Never reverse polarity, or damage might occur to the diodes in the alternator. Don't run the engine with the alternator's output disconnected. Never short or ground any terminal in the charging system unless the instructions in the shop manual indicate otherwise.


About the Author

A reporter since 2005, David Eiranova wrote for "The Lunenburg Ledger," from 2007 to 2009 and has served as a correspondent for "The Lowell Sun." He holds a Bachelor of Arts in economics. Since 2007 he has been the director of publicity for the Acton Community Chorus.

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