Basic Techniques to Troubleshoot Your Car's Charging System

The charging system in your vehicle is responsible both for maintaining the charge of your battery and for providing electrical power to the vehicle's systems as you drive. Confirming that a charging component is failing is easy, but recognizing the early signs of trouble can be difficult.

Know the Difference Between an Alternator & Battery

Many people confuse the roles played by the alternator and the battery in a car's charging system. The battery's primary role is to store energy while the car is turned off. This energy is utilized to run the starter whenever you crank the engine. Once the engine is running, the alternator takes over and the battery is relegated to a secondary role.

Since the alternator is not producing electricity until the car is actually running, it is usually safe to rule it out as the cause of no-start or hard starting issues. Likewise, failing batteries will rarely produce driveability issues or noticeable electrical problems while the car is in operation.

Know the Symptoms of a Failing Battery

Your battery's job is to hold sufficient charge to run the starter motor for long enough to get the engine going. The battery's ability to hold a charge will decrease as it nears the end of its life, and this usually produces obvious symptoms.

A completely or nearly dead battery will often fail to turn the starter motor at all, leaving your car stranded. In some cases, the battery may be drained so fully that interior electronics won't work.

Many people are quick to blame slow cranking or excessively long crank times on the starter, but often this is a sign of a bad battery. Always have your battery tested before condemning your starter or other expensive components.

Batteries are consumable components that should not be expected to last more than three or four years, so the best way to avoid trouble is to make battery testing a regular part of your maintenance routine. A battery older than four years should be tested or replaced as preventative maintenance.

Know the Symptoms of a Failing Alternator

Once your engine is running, the alternator's job is to provide a steady flow of electricity to operate your car's electrical components and keep the battery fully charged. A failing alternator can produce a wide range of seemingly unrelated symptoms, so it's important to be aware of it as a potential source of trouble.

Lights dimming at idle or varying in intensity with engine speed indicate that your alternator is not functioning properly. You may also notice climate control fans that speed up or slow down as you rev the engine.

As counter intuitive as it may seem, a dash light that looks like a battery usually means alternator trouble. Most cars are not equipped with warning lights to indicate battery problems.

Modern cars rely heavily on computer control, so a failing alternator can sometimes produce symptoms that do not seem related to the electrical system. Engine hesitation, rough idle, and even stalling can all potentially be the result of an alternator producing low or inconsistent voltage.

A grinding noise from the alternator likely indicates that the alternator's bearing is failing. This is a common failure mode for alternators and should not be ignored, even if there are no other symptoms present.

Since your car's alternator is belt-driven, worn and slipping belts can prevent the alternator from functioning properly. If your belts appear worn, or if the above symptoms are accompanied by squealing, consider replacing your belts as a first step. If your belts are good, you should proceed to have the alternator test.

Troubleshooting Strategies

The best way to diagnose any car problem is to rule out likely causes by testing suspicious components. Throwing parts at a problem is expensive, time consuming and rarely produces good results. Many auto parts store offer free testing of alternators and batteries, so there is no good reason to replace components blindly.

Use the above information to identify which failures most closely match your car's symptoms and proceed to systematically test components until you find the problem. With a little knowledge and effort you can save yourself time and money and fix your problem properly the first time. For more assistance, consult expert resources such as AERS Auto Electric & Refrigeration Ltd.


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