Two Tests for Repairing a Faulty Alternator

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09 Sep 2019

Category:

Alternators are an integral component for keeping your vehicle mobile. When confronted by a faulty one, it is essential to properly carry out the necessary tests for finding the source of the issue so you can get back on the road as soon as possible.

When it comes to alternator faults, the root cause can typically be traced back to the battery. Several issues related to vehicle batteries prompt the warning lamp on the vehicle dashboard to illumine, indicating a charging circuit fault. When approaching a potential charging system repair, you should first check for any recorded fault codes and carry out a full battery condition test. We recommend that you then use a voltmeter to confirm the charge voltage at an engine speed of approximately 2,000rpm with both lights and heaters turned on for a complete stress test.

Here are two tests you can also use to determine the route of your alternator repair:

 

Voltage Test

For an accurate measurement of your charging system’s voltage, attach the voltmeter to the positive and negative battery posts.

Reading Lower than 13V

Your battery is weak or has damaged/loose belts that may be causing a low alternator output.

Reading between 13V and 15V

A reading within this range is considered optimal for a vehicle battery.

Reading Higher than 15V

A reading this high may be caused by a faulty regulator. If your reading surpasses 15V, do not operate your vehicle under any circumstances. This will ensure your safety and your vehicle’s wellbeing.

 

Battery Cable and Connection Test

Ensuring that the connections to your vehicle battery are clean, well-fitted and free from corrosion will allow them to perform at their best. You can use your voltmeter to assess both the positive and negative battery cables using the following methods:

Positive Battery Cables

Measure from the alternator output terminal to the positive battery post. If your reading is higher than 0.35V, this indicates an issue with the positive side of the charging circuit. Carefully examine the circuit for any damaged cables or corroded terminals.

Negative Battery Cables

Measure from the alternator case, ground and negative battery post. If your reading is higher than 0.25V it could indicate that the negative battery cable or connection to the frame/chassis engine block is loose or corroded.

 

Once you figure out what is causing your alternator fault, carrying out the requisite repair can be a simple matter for novice and professional installers. When working with an operating engine, however, make sure to exercise extreme caution. Protecting yourself against harm is the top priority during any repair, and even carrying out these initial tests can be dangerous if done incorrectly.

For more NAPA Know How or to explore our range of alternators, take a look at the rest of our website.

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