Electrical Repair: How To Diagnose & Repair Your Charging System Part 2

In part 1 of this series, we gave an overview of the charging system, and discussed your vehicle battery and how to test and troubleshoot it.

Assuming that the battery is known to be good, the next step is to make sure that the battery terminals are clean and tight. If either of these terminals are loose or excessively dirty, unwanted electrical resistance will be the result and can cause a variety of problems.

The next item to test is the charging voltage at the battery terminals. This is a simple test and is done by connecting a DC voltmeter(a digital multimeter set to read DC volts is fine)across the battery terminals while the engine is running at a moderate idle, say 1200-1400 RPM. The voltmeter should read 13.8 to 14.5 volts and be steady.

If the voltage reading is substantially less than 13.8 volts – say for example it reads 12.5 to 13.0 volts – then the next item to check is drive belt tension. An alternator drive belt which is too loose and/or defective can cause a low or no charge condition.

Many modern vehicles are equipped with non-adjustable automatic belt tensioners which maintain correct drive belt tension. A telltale sign that an automatic tensioner is at work is if the vehicle uses a wide, multigrooved belt, often called a serpentine belt. If your vehicle is so equipped, then belt tension is likely not the problem.

At this point, you should obtain a  service manual for your vehicle. Online service manuals are available for most vehicles nowadays so you don’t have to wait to get the information.  The  service manual will tell you whether or not your vehicle contains a voltage regulator which is seperate from the alternator, or is a part of the alternator. Another way to find out is to call your local dealer or auto parts store and ask if your vehicle uses a seperate voltage regulator. In part 3 of this series, we’ll cover both types and what to do. Go To Part 3