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Fixing a Problematic Alternator


09 Sep 2019

Category: Guides

Any problems with the alternators can be directly linked to a problem with the battery so it’s important to cover off the below tests and checks.

Several issues related to the battery can cause the warming lamp to illuminate on the vehicle dashboard indicating a charging circuit problem. In this instance, technicians are always advised to use a voltmeter to isolate a faulty component within the charging system.

In order to test the circuit, technicians should look at performing all two tests while the engine is running at about 2,000rpm, with the lights and heater switched on.

Voltage test

Measure the voltage from both, the positive and negative battery post. The optimal reading is any from 13 volts to 15 volts. If a reading is too high, it may indicate that there is a bad regulator and the vehicle must not be operated.

A reading below 13 volts is indicative that a battery is weak or damaged/loose belts that may cause a low output from the alternator.

Battery Cables & Connections

Battery connections should be clean, tight and free of corrosion. To ensure that this is the case, tests can be conducted to the positive and negative battery cables:

Positive Battery Cables – Take a voltage measurement from the alternator output terminal to the positive battery post. If the reading is higher than 0.35 volts, it is indicative of a positive side of the circuit. Take care and look for damaged fuses, cables and fuse links if the reading is higher than 0.75 volts.

Negative Battery Cables – A reading of more than 0.25 volts when a voltage measurement from the alternator case, ground and negative battery post may mean that the negative battery cable or connection to the frame/chassis engine block is problematic.

WARNING: Always practice extreme caution when working with an operating engine.

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