Electrical Repairs Demystified – How to Troubleshoot Your Vehicle Charging System

Vehicle charging systems haven’t changed much over the last few decades. But with the increasing complexity of the modern automobile, along with the addition of many aftermarket accessories such as cell phones, DVD players, high-power audio systems, alarms etc., the role of the charging system is now more important than ever.

The charging system on your vehicle can be thought of as a small power plant which does exactly what its name implies – charges and maintains a good state of charge on the battery. The charging system will normally consist of two major components: An Alternator which actually supplies the necessary electrical current in order to charge the battery, and a Voltage Regulator. The latter insures that the system does not overcharge the battery, and that the correct system voltage is maintained. Most vehicles produced within the last 20-30 years use a voltage regulator which is an integral part of the alternator itself. This article assumes that your vehicle uses this type of alternator.

If your vehicle is showing symptoms such as dim lighting, “dragging” during engine starts, or frequent dead batteries, then the charging system may be at fault. Although it may seem obvious, the first item to test is the battery itself. A defective battery in an otherwise healthy electrical system can cause any of the above mentioned symptoms. Testing the battery is a simple procedure, and can performed quickly by most auto parts stores, repair shops, dealers, and even some large department stores. You can also perform the test yourself if you have access to a Battery Load Tester, a device which is made for the purpose. The load tester works by placing a specific amount of electrical load on the battery for a specific amount of time while monitoring the available battery voltage. The battery should be fully charged before the test in order to insure accurate test results.

Assuming that the battery is known to be good, then the next item to check is the battery terminals – the actual points at which the battery is connected into the electrical system. It is very important that these connections are clean and tight. This simple thing is often overlooked as a source of trouble, and is also a frequent cause of such trouble. Visually inspect the terminals, and clean and/or tighten them if needed. To clean, use a small, stiff wire brush or a terminal cleaner which is made for the purpose. You can buy these at nearly any auto supply store, and most hardware stores. You will also need an appropriate sized wrench with which to remove the battery terminals. Important: Always disconnect the negative (-) battery terminal first, and reconnect it last. This will help to keep from shorting the battery while connecting or disconnecting the terminals and possibly causing damage and/or personal injury.

If the battery terminals are clean and tight, then the next item to check is drive belt tension. If the belt which drives the alternator is too loose, then the alternator will not produce enough electrical current to keep up with demand. Many modern vehicles utilize a single belt which drives the alternator and other accessories. This system usually also has an automatic belt tensioner which always maintains correct tension and is not adjustable. If your vehicle uses a wide, multigrooved or so-called “Serpentine” belt to drive the alternator, then it likely also has an automatic tensioning device.

If your vehicle does not use an automatic tensioning device, then check belt tension as follows: With the engine turned off, grasp the belt at a convenient point about 8 to 10 inches from the alternator pulley. Move the belt slowly up and down. The belt should not move more than about 1/2 inch. If the belt seems to be excessively loose, then of course it will require tightening and/or replacement.

If belt tension is correct, then the next item to check is the alternator itself. You now have two choices – you can test the alternator yourself with a simple test using a voltmeter, or you can have the test performed by a professional. If you choose to do the test yourself, then you will need a DC voltmeter, or a multimeter. Such a unit can be purchased at most auto supply stores, hardware stores, department stores, home improvement stores, etc.

The test procedure is quite simple. Set the meter to read DC volts, and set the correct range if needed. Some meters will select the correct range automatically. Nearly all meters will come with instructions on how to set them to read DC volts. Next, connect the meter across the vehicle battery, positive (+) to positive (+) and negative (-) to negative (-).

With the engine running at a moderate idle – say 1200 to 1500 RPM, the meter should read approximately 13.8 to 14.8 volts and be steady. If the reading is substantially outside these figures and all other items mentioned have been tested and verified good, then the alternator is likely defective.

By having done the simple tests which are outlined in this article and further isolating the cause of your charging system trouble, you can often save money at the repair shop by specifying which part(s) need to be repaired or replaced.