There was once a time when a technician only needed a voltmeter to diagnose a battery. But charging systems have changed. In this video, Tire Review’s Maddie Winer discusses the ways in which charging systems have changed, from the Tire Review Continental Tire Garage Studio at Babcox Media.
In today’s vehicles, the alternator and battery have a mutually dependent relationship. When a vehicle’s engine is on, the alternator charges the battery, and in fact, fuels all of your car’s electrical systems.
While the battery gets fuel from the alternator, the alternator is managed by the vehicle’s engine control module, or ECM. That means nowadays, testing the battery and alternator now requires a scan tool.
Why? Well to determine what the cause of a battery issue really is. For example, sometimes only the battery voltage is present at the battery on a running engine, but this doesn’t mean the alternator is “bad.” It just means it’s charging.
For some vehicles, it’s normal to see a reading as high as 15 volts on a battery. For others, it’s normal to see as low as 13 volts. And still for others,, it’s perfectly normal to see the alternator not charge at all intermittently while some are controlled only with an internal or external regulator. Not knowing what controls what and how it is supposed to function, can cause a misdiagnosis or a critical problem to be overlooked. This is why a can tool should be used. As alway, be sure to take time to look at the service information.
If you don’t see at least 13 volts when you check charging voltage at the battery with the engine idling, check the wiring connections at the alternator — not just visually or by wiggling the wires or connectors. Check it for excessive resistance by doing a voltage drop test. Many so-called alternator problems turn out to be nothing more than a bad connection at the alternator or a bad wiring harness.