Symptoms of a Bad Alternator
Updated 10 months 1 week ago
Getting stranded on the side of the road because of a bad alternator is never fun. Don't let that happen to you. Before an alternator fails it will give you enough warning signs to let you know it's going out. Symptoms that your alternator is going bad may vary because an alternator can fail for several reasons including a bad diode, bad voltage regulator, worn brushes, bearings going out or simply get seized. Regardless of the reason why your alternator fails, in most cases, the warning signs are there before an alternator fails.
In this article, we will review common symptoms of a bad alternator. Steps you can perform to check an alternator and charging system yourself using a Charging System Analyzer.
Symptoms of bad alternator
An illuminated battery warning light on the instrument cluster is the first signs to the driver that there is an issue with the charging system.When the battery light is displayed it is best to give it attention as soon as possible. If the alternator fails, your car will only run for about 10-20 minutes on the battery and die.
Loss of power
If there is a complete loss of power; there is a good chance that the alternator failed. Especially if the battery warning light or alternator symbol show up on your instrument cluster and your car dies a few minutes later. To check for a complete loss of power, turn on your headlight, dome light, radio and so on to check for power. If there is no power, your alternator has failed. When this happens the car may start and run if jump started, but as soon as the jumper cables are disconnected the car dies.
A failing alternator will start to make a loud whining noise at idle and the whining noise will increase with engine speed. Bad alternator sound can be confused with bad power steer pump noise.
How to tell bad alternator noise vs. power steering noise?
- Alternator noise is not as loud as power steering pump.
- Alternator noise increases when engine RPMs change.
- Power steering noise increases when steering wheel is turned
- A bad alternator will have a burning smell. Power steering pump does not.
In addition, an alternator can also make a growling noise due to bearings inside the alternator. If the bearings start to fail; eventually the alternator itself will fail.
Not Charging due to Belt
The drive belt is responsible for turning the pulley on the alternator. Without the drive belt, the alternator will not be able to charge the battery. Sometimes a slipping belt can cause a decrease in power or a bad drive belt tensioner can also cause a belt to slip. In addition, cracked, brittle, torn belt, contaminated belt due to oil or power steering fluid can contribute to a decrease power. Moreover, sometime you will lose power altogether if the drive belt snaps in half.
If you smell a burning smell that smells like rubber is burning, which means your alternator is seized. Usually, when this happens, the belt will snap and burn off completely. At this point, the alternator needs to be replaced with a new one and most likely it is difficult to rebuild the alternator at this point. Moreover, you may want to inspect the drive belt tensioner, drive belt pulley and so on for drive belt rubber that may leave residue behind. If there are; I recommend cleaning the tensioner and pulley with brake cleaner or carburetor cleaner. Furthermore, inspect the tensioner and pulley by turning it making sure it wasn't damaged from a seized alternator.
Bearing Going Out
On high mileage vehicles, it is common for the bearings to fail. Alternator bearings take time to wear out and typically you will get plenty of warning signs. Common symptoms that the alternator bearings are wearing include squealing sound that may get louder as the engine RPMs are increased. If a vehicle is parked for an extended of time it can cause the alternator bearings to bind or seize. When you start the car you will notice a grinding or granting noise coming from the alternator due to a bad bearing. In rare cases where the alternator with bad bearings is ignored for so long, it can cause the alternator to catch fire due to overheating of the bearing.
Symptoms of bad alternator can vary between different makes and models. For example, symptoms of bad alternator may include low voltage fault codes on various control units. Airbag / SRS light on instrument cluster turns on for no apparent reason and no accident. A vehicle going into limp mode. Automatic Transmission may get stuck on 1st, 2nd or 3rd gear due to a bad alternator.
Bad alternator vs. battery
The main components of the charging system include the alternator, alternator wires, battery, voltage regulator. Sometimes it can be difficult to tell if you have a bad battery or bad alternator.
Watch a video on how to perform battery, alternator and charging system test. This test will also help you determine if the battery is bad or if you have a bad alternator.
In this case, we are using Foxwell Battery Analyzer but any battery analyzer will work.Back to top
Troubleshooting bad alternator
One method to test the alternator is to perform a charging system test. This is a common test performed at dealerships and auto repair shops. Testing the alternator and charging system is very easy DIY if you have a Charging System Analyzer. A charging system test will help you determine if your alternator is failing or has low output. It will not alternator problems such as worn bearings.
Check alternator voltage
Modern vehicles will turn on the battery warning if the battery voltage is low. This can be common at startup especially during winter or if the secondary battery is not fully charged (when applicable). One of the first recommendations is to check the battery voltage. With the engine off, the battery voltage should have a minimum voltage of 12.2 volts and a maximum voltage of 12.6 volts. However, the battery voltage can stay above 12.6 due to surface charge if your vehicle was recently running. To remove the surface charge, turn on the headlights for a good 30 seconds then turn it off. Check the battery voltage again, if the battery voltage is good then move on to the next step.
The alternator is responsible for charging the battery and bringing it up to 100% charge. Get yourself a multimeter and set it to voltage. With the engine running, check the battery voltage. The battery voltage should be around 13.5 volts to 14.5 volts. The voltage should not be below 13.5 volts which means you have a weak alternator and over 14.5 volts is overcharging. If the voltage is not within range move on to the next step below.
Check charging system wires
A bad alternator wire or corroded battery terminal can prevent current from flowing properly. Use a multimeter and set it to the ohm setting. Check the ohms from the wire from the alternator 12-volt terminal to the battery. Resistance should be less than 0.5 ohms. Anything greater means there is high resistance. If you get a reading of zero that means there is an open in the wire. Sometimes there is a fusible link between the alternator wires and battery. Check the fusible link and make sure it is not blown. If the fusible link is not blown, check the condition of the wire.
Check alternator bearings
An experienced mechanic will be able to tell if a car has bad alternator bearings just by listening to the alternator. If you suspect your alternator bearings are going out, stop by a trusted auto mechanic and ask them to listen to your alternator while the engine is running.
The other option would be to remove the serpentine belt/drive belt that turns the alternator and start the car. Does the noise go away? If the noise goes away when alternator belt is removed, you know the alternator is the culprit. Also, check for play at the alternator pulley for excessive play.Back to top
Alternator Repair Cost
Typical cost to replace the alternator at the mechanic varies between $380-$600 for an aftermarket alternator. Replacing the alternator with an OEM one can cost between $600-$1300 depending on the make.
DIY cost to replace the alternator yourself is typically between $100-$200 for the alternator. Aftermarket alternators can be purcased online for any car if you are looking to save money.
Search aftermarket alternator for your car.
Don't ignore symptoms of a bad alternator. If the alternator fails not only can your car catch fire but most commonly you will get stranded on the side of the road. The serpentine belt may also break causing additional damage.
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