The Definite Guide On How To Test Your Car’s Alternator [2021. Updated]

There are different ways in which problems with the alternator can manifest.


These are often dependent on the type of problem or issue with this part of the automobile.


Perhaps your car gives off an odd smell, a dash light comes on or you hear a growling sound coming from under the hood.


The fantastic thing is that analyzing the existence of an alternator issue is relatively straightforward.


All you will need is a voltmeter or multimeter and some other items, and you are on your way to diagnosing a problematic alternator.


This is the complete guide to analyzing the alternator in your car.



When noticing a first symptom, you must act quickly to avoid worsening.



Typically, analyzing the alternator can be performed by yourself without searching for a trained mechanic.


Why Test Your Alternator


It’s clear that the alternator is an important part of a modern vehicle’s electrical and charging system.


The alternator also forces up the automobile’s electric system during performance. It recharges the battery of your car to keep it working.


The alternator also powers up the car’s electrical system during operation. If there is a problem with the alternator, then you will experience a reduction in the functionality of electrical systems.


You will notice your headlights getting dimmer than usual. This may be harmful when driving at night or in zero-visibility conditions.


You might not have electricity to power your air conditioning unit or your car’s cabin heater, making your ride excruciating.


Your car entertainment system will also not supply you with a remarkable experience.


Any element on your car which needs power will begin to malfunction, which is why you should check the condition of the alternator to make sure that it can generate sufficient energy to operate different electrical components of your car.


Thus, if you find a battery warning indicator light on your instrument panel, then it’s almost always a fantastic idea to check the voltage output of your vehicle.


Testing the Alternator with a Voltmeter


One of the easiest ways to test the condition of your alternator is by using a very simple device called a voltmeter.

Here’s how to perform the test.


Measure the Base Voltage of the Battery


1. Ensure your battery has a complete charge.
2. Buy a cheap voltmeter and place it to DC style at 20 volts.
3. Be certain your voltmeter has new batteries to get more precise readings.
4. Check whether the system registers 0.000 volts over the screen.
5. Watch out for the colour-coded wires of your voltmeter.


Ensure the battery terminals are free of residue or other debris.


When the terminals aren’t clean, it may result in inaccurate ion readings.


Join alligator clips or even the probe ideas for their battery springs: positive to negative and positive to negative. Upon contact, you must observe the alteration in the voltmeter screen.


A fully-charged automobile battery will have around 12.6 volts.


Look out for the value.


In case it helps, you might choose to write it all down. When there’s no problem with your battery life, then you might wish to have it load-tested.


Remember that analyzing the alternator demands a fully-charged battery.


Measure the No-Load Voltage of the Charging System


Get a helper to start your vehicle’s engine.


Allow the engine to run for a little while you’re idle.


Ask your helper to keep up the rate of the motor at 1500 RPM. Also, tell your helper to switch off each of the car’s accessories.


Switch off any car lights, such as those from the tool panel.


Turn off the stereo and other accessories which may run on power.


If the growth is more significant than 2.0 volts or 14.7 volts on the voltmeter screen, it may signify you there’s an issue with your alternator.


This may signal an issue in your vehicle’s alternator or its electric system.


When there’s absolutely no noticeable shift in the voltmeter reading, you likely have a poor charging platform, which is also true when the voltage output signal is lower than your foundation battery voltage reading.


Check that your system’s connectors and wires are in good shape. If the voltage reading stays the same, you might have an issue with your alternator or the voltage regulator.


Measure the Load Voltage of the Charging System


Restart your engine and allow your helper to keep the motor speed at 2000 RPM.


Switch on all your automobile accessories like the wipers, headlights, ac, and radio, amongst others. Reconnect the voltmeter and see the screen.


In this evaluation, you will attempt to ascertain your system’s charging voltage.


Thus, you will subtract the foundation battery voltage reading from the loading voltage reading.


A charging voltage of 0.5 volts greater than the baseline reading is perfect. Some put the critical levels at 13.0 and 15.0 volts.


Anything lower or higher than these values can point to a faulty alternator.


Test the Alternator Diode


To check for a bad alternator diode, you may want to reset your voltmeter to the lowest possible AC voltage scale setting.


Have your assistant start the car’s engine and let it run for a few minutes at 1200 RPM.


Connect the voltmeter probes on their respective battery terminals. You should read “0.00” in the display.


If there is a fraction of a volt in the display (i.e., 0.001 volts), it only means you have a bad alternator diode.


Unfortunately, you cannot replace the diode alone.


You will need to replace the entire alternator.


Testing the Alternator When You Don’t Have a Voltmeter


Using a voltmeter is one of the most practical and most accurate ways to determine the condition of your car’s alternator. However, it is not the only test available.


You can also evaluate your alternator without ever using a voltmeter. Here’s how.


Assess the Condition of the Alternator Drive Belt


The alternator draws its power by the motor’s mechanical power through the drive belt, which links to the alternator.


One way you can check for the integrity of this alternator is by assessing this drive belt.


A second-hand driveway belt, along with a loose belt, may result in charging problems.


Listen for a Characteristic Sound from the Engine


If you attempt to observe your engine when it’s running, you might notice a very different sound.


Mechanics explain the sound like a loud snapping noise. It’s frequently a symptom of a debatable alternator.


Perform the Headlight Test


It’s best to execute the headlight test in darkened surroundings so that you may assess the brightness (or dimness) of your headlights.


Switch on your vehicle’s headlights and take notice of its brightness.


Then start your motor.


You might observe the brightness of the headlight fade just a bit. After a time, nevertheless, it ought to return to its original brightness level.


If you aren’t sure about how to check your alternator, a mechanic is always a fantastic person to call.


As simple as it is to check out an alternator, there might be several things that need a more specialized evaluation.


How much does the problem with an alternator  cost?


You will need a voltmeter, which is available from Amazon for about $49.00 if you don’t have one already.


A local repair garage or dealership can charge as much as $145.00 to test the system.


Final Thoughts


If your vehicle is slow to start or does not start at all, check your vehicle battery and alternator, since these are probably the culprit.


Even better, don’t wait until your vehicle is slow to start or even does not start; you have to inspect both of these critical components frequently, or perhaps you will end up late for work or stranded in the middle of the street.


It’s crucial to listen to what your car is attempting to tell you.


Any odd symptoms are probably pointing to some malfunction somewhere and must be dealt with immediately.


Don’t leave it until it is too late.

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