How To Diagnose A Bad Alternator

Sometimes it happens, we turn the key to start the engine and after some slight rattles we cannot start the engine, is the battery dead or is it a more complicated problem and the alternator is giving problems?

How To Diagnose A Bad Alternator

This situation can continue to happen if the battery is changed and could be the cause of an alternator failure.

In this article we are going to analyze the clues that can indicate this malfunction and what to do to solve it.

How does a car alternator work?

car alternator
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The alternator is basically an endless generator of electricity in vehicles.

It takes a lot of energy to start an engine and meet all the electrical needs of a vehicle.

While different batteries can have enormous capacities, eventually the headlights, heater, radio, navigation, and other components will deplete battery power.

An alternator charges the battery while the vehicle is running by converting mechanical energy from a rotating pulley into current.

The rotor, brushes, and other internal parts of an alternator wear out over time, so replacing it is something that must be done eventually.

The following symptoms should give an idea of ​​what is wrong, but we recommend taking the vehicle to your trusted workshop for load testing and system start-up.

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Symptoms of alternator problems and failures

Dim lights

The faulty alternator symptom that most drivers recognize is dim or flickering lights.

This is really obvious when the headlights are on at night, but it is also noticeable in the dashboard lights and in the interior center light.

If the lights illuminate as the RPM increases, it is an even safer sign.

Service Engine Light

Another obvious signal is what the vehicle is trying to say through the dashboard.

This varies by model, but when the alternator begins to loosen, it may light a “Check Engine,” or a battery icon indicator.

Strange noises

The serpentine belt could have stretched with age and it might not turn the alternator pulley effectively, causing a lack of load.

This normally results in a squealing noise.

On the other hand, the internal bearings can wear out, causing a grunt or grinding noise.

Electric problems

Vehicle electrical equipment, such as power seats or windows, may run slowly.

Without enough power, sometimes the device will not work or will suddenly stop working, as if the radio was turned off.

Engine stop

If the engine suddenly shuts down while driving, it could be an alternator problem.

Fuel injection requires a fair amount of electrical power, and without it the engine stalls quickly.

Dead battery

Without a working alternator, the vehicle quickly uses up the battery’s full capacity, leaving it drained.

The hood would have to be opened and the battery checked.

A new battery and a malfunctioning alternator will bring the vehicle to a standstill again.

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How to diagnose a bad alternator?

how to diagnose bad alternator
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If the vehicle has a “Check Engine” light, connect a code reader to the diagnostic port.

If the P0562 code appears, it is very likely that the alternator is in bad condition (it should be noted that the codes may vary depending on the make / model / year of the vehicle). If an alternator is suspected of failing but does not have a warning light, raise the hood and check the condition of the belt.

If it is glazed and has a slightly burnt appearance, it is an indication that it is slipping. Belt is too loose so it slides over pulleys instead of running on them. The friction of metal on rubber heats the belt, wearing it quickly.

The tensioner must be adjusted to get just the right tension (too tight can also damage an alternator’s bearings), or simply the belt should be serpentine. If everything looks fine under the hood, it can be checked with a multimeter.

Make sure the vehicle is parked on a level surface with the parking brake set and wear safety glasses. The meter is set to 20 VDC and connected to the leads to the battery: positive lead to positive battery terminal and negative lead to negative terminal. It should read around 12.6 volts.

We start the engine and carefully recheck the voltage. This time, it should be at least 14.2 volts if the alternator is working properly and charging the battery.

If the voltage is good, turn on the headlights, interior lights, radio, heater, and any other electrical loads. The meter should still show more than 13 volts. If any of the voltages are below specification, the alternator should be replaced. All cables should also be checked for corrosion or a loose connection.

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