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How to Test the Car Alternator

Model: (Various brands) Various
Part: Alternator

Video tutorial

The alternator of a car is responsible for supplying electrical power and recharging the battery; it is therefore important to periodically check its operation. A first check occurs when you start the car: when you turn on the ignition, a red battery warning light will appear.

Once the engine is started, the light goes out, indicating that the alternator is functioning. For a more thorough test, you need a digital multimeter set to DC volts.

Open the bonnet and place the probes of the multimeter on the corresponding terminals of the battery: if the voltage is above 12.50V with the engine off, the battery is fine. Now start the engine and turn on high-load devices such as the lights and air conditioning: you will see the multimeter still registers a voltage above 12V. Accelerate to 2,000 RPM and you will see that the voltage increases.

Now turn off the devices and observe that the values will stabilise between 13.50 and 15.00 depending on the car model.


Updated on 15 July 2026 by ScegliAuto


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by ScegliAuto

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