How to check the alternator voltage output is one more simple check-up you can do on your own.
But, as you’ll see there’s no special skill needed. The most important thing is to have some goodwill, time, and a multimeter.
If you don’t know how to use a multimeter, you have an explanation under the step-by-step procedure.
Below, you have other explanations and advice on this topic (symptoms of bad voltage output, what to do if the alternator voltage output is high or low, etc.)
Also, you can watch the whole procedure on our YouTube channel or at the end of this article.
How to check the alternator voltage output –step by step procedure?
Open the hood (bonnet)
Find the battery location
Battery location varies from car to car model. It’s mostly located in the engine bay, but also in the trunk or under the windshield. Anyway, it’s mostly in a visible place so it should be easy to find.
Open the battery casing-holder
Use the multimeter
Set the voltage reading on the multimeter to 20 volts DC (direct current)
The car battery, installation, and devices all work on 12 volts. There will be no setting for 12 V exactly so set to the next bigger number and that will be 20 volts. Don’t go under that.
If you go over 20 V nothing special will happen except that the decimals on the screen will move and it will be harder to read the output voltage.
Connect the tester cables on the multimeter to the battery poles
You’ll see that the tester cables are (mostly) red and black. Connect the red one to the “+” battery pole and the black one to the “-“pole.
You’ll immediately get a reading of the battery voltage. If everything is OK the battery voltage should be around 12.2 to 12.7 volts, depending on the condition of the battery.
If the voltage is lower, you’re probably looking at a car battery replacement in the near future.
Start the engine-make sure that you’ve put the multimeter in a safe place.
Put the multimeter in a safe place, especially if the car battery is under the hood. If the multimeter falls into the engine bay while the engine is running, it can damage or crush the digital multimeter.
Take a reading: 13.5 volts to 14.5 volts is OK!
13.5 volts is the bare minimum. Under that and the car installation and battery isn’t getting enough electric power. Over 14.5 volts can cause serious damage to the alternator and car battery.
After taking the voltage output reading, remove the tester cables from the battery poles and remove the multimeter.
Close the battery casing-holder. Make sure the lid of the casing sits in properly.
How do I use the multimeter?
A multimeter, as its name says is a multi-purpose instrument for taking measurements of electric voltage, amperage, resistance, etc.
There are two basic types: analog (with a pointer needle) and digital.
Both do a good job. I recommend the digital multimeter as you can get a more accurate and readable measuring.
Using it is very simple. Two things important to you:
- The battery testers – they’re connected to the multimeter with cables. The testers give the multimeter information it needs to make a reading.
The two colors (mostly red and black) are for the “+” and “-“side of the electric current.
- The setting switch (round switch on the digital multimeter) – its purpose is to switch to whatever kind of reading you need (voltage, amperage, resistance, temperature, etc).
So, turn the multimeter on, turn the setting switch for whatever reading you need and connect the testers. Simple as that.
Why is it important to check the alternator voltage output?
- to realize on time that you have a problem (alternator, installation, etc.)
- to prevent further damage to your car installation, electronics, car battery, etc.
- easier diagnostics of what the possible malfunction is.
You can make this check even if everything is OK with your car, it can’t hurt. It’s even preferable to do this at least two times a year.
The main thing to know is that when you see that the voltage output is not OK; take action as soon as possible.
Neglecting this kind of problem can get you in trouble (like not being able to start or drive the car) and cost you a lot of money to repair (3-4 digit numbers on the repair bill).
When should you check the voltage alternator output?
Here are some sure signs that it’s time to make this checkup:
If the alternator voltage output is low you’ll get:
- You’ll get the warning light on the dashboard (car battery icon)
- Poor cranking when you want to start the engine (although you’ve replaced the car battery)
- Weak and dim headlight beams.
- Sudden problems with electronics-you get all sorts of “gremlins” (like random check lights or else). An irregular voltage output has been known to send people and mechanics on a wild goose chase more than once.
If the alternator voltage output is high you’ll get:
- An unpleasant, sulfur smell from the car battery
- Headlight lamp bulbs tend to burn out more than usual.
- Also can cause unusual behavior with car electronics.
What should I do if the alternator voltage output is too low?
Check the condition of the ribbed belt
If the ribbed belt is in bad condition it will cause slipping of the alternator pulley.
Since the alternator depends on the engine drive and the belt is the only thing that connects the alternator to the engine, slipping will cause the alternator to produce less electric energy.
Check the electric connections on the alternator (if the alternator is in an easy-to-access-place).
All of the wires that lead to the alternator have to have a good and clean connection. A broken cable is a common fault, especially with older cars.
Clean the battery poles.
Over time a thin oxidized coat forms on the battery poles. Disconnect the battery terminals and clean them with some sandpaper or a small file. This will ensure that the vital connection from the alternator to the battery is in good condition.
Check the ground wiring
This is the “-“ (minus) part of the installation and is mainly connected to the car body. Not having a good ground connection in the installation can also cause many problems. See that all the ground cables have a tight and clean connection.
What should I do if the alternator voltage output is too high?
In this case, you’ll probably need an alternator repair and besides that, there’s nothing much more you can do.
This is mostly due to two things:
- The voltage regulator is faulty thus sending two much electric power to the car installation, devices, and battery
- A burnt-out alternator stator.
How long can I drive with an alternator problem?
If the alternator voltage is too low:
The car then uses power from the battery. This can last only for some time before the battery is depleted (especially if you’re driving with the headlights on). After that, the car will “die” on you.
If the voltage is too high:
the more you drive, the more damage you cause. You’re risking car installation overload, damage to the car electronics, and damaging the car battery (so much so that you’ll have o buy a new one).
Should I repair the alternator myself?
If you don’t have advanced knowledge of mechanics and car electrics, don’t do it.
Any kind of repair will demand taking the alternator off the car, disassembling it, fixing what’s wrong, assembling it, and then re-installing it on the car.
This is under the condition that the alternator is in an easy-to-access-place. In most present car models, because of the cramped engine bays, getting to the alternator mostly is a big headache.
There is also the problem that many of the present alternators are not repair-friendly. You see, there was a time when the alternator could be “pulled” apart, properly maintained, and returned.
Nowadays it’s all sealed and riveted in a way that makes repairs almost impossible.
If you’re going to DIY the alternator repair and have some basic mechanical skills, try buying a new or used complete alternator and do the replacement in this manner.
This way, a good outcome, and quality repair are much likely.
HOW TO CHECK THE ALTERNATOR VIDEO