The alternator is the backbone of your vehicle’s electrical system, silently keeping everything from headlights to your windshield wipers running as intended. Despite its major role, many drivers overlook this component until it’s too late.
A failing alternator can quickly turn a routine drive into a roadside emergency, leaving you stranded at the worst possible times. Understanding the common causes of alternator failure and recognizing early warning signs can save you from unexpected breakdowns and costly repairs.
Purpose of a Car Alternator
The alternator serves a very important purpose in your vehicle. Its primary function is to generate the electricity needed to power all of the vehicle’s electrical components and recharge the battery. This is accomplished by converting the engine’s mechanical energy into electrical energy.
Without a functioning alternator, all electrical components would rely solely on the battery for power. However, the battery alone isn’t capable of providing enough electricity for extended periods. In fact, with a bad alternator, a car might only run for a few minutes before the battery is depleted and the vehicle loses power completely.
Common Causes of Alternator Failure
When people experience electrical issues with their vehicle, they’re quick to think it’s the battery’s fault. But if you have a newer battery and you’re still having these electrical problems, then it’s likely the alternator that is at fault.
Here are some of the most common causes of an alternator going bad:
1) Normal Wear and Tear
This one’s pretty obvious. The typical lifespan of a new alternator is somewhere in the 5 to 8 year range. If it has been that long and you have electrical issues, then your alternator may simply be worn out and needs to be replaced.
If you suspect the blame may fall on your battery, keep in mind that they typically last 2 to 5 years. Hot climates can shorten this to around 2 years, as heat accelerates battery degradation. Alternators, however, are generally not affected by temperature, so their lifespan remains consistent across different climates.
Related: Symptoms of a Bad Alternator
2) Computer System Malfunction
Modern vehicles rely heavily on sophisticated computer systems, such as the Engine Control Unit (ECU or ECM) or Powertrain Control Module (PCM), to manage nearly all vehicle components, including the alternator. A malfunction or glitch in these systems can prevent a perfectly good alternator from charging properly.
In such cases, it’s almost a given that you’ll notice other electrical or driveability issues as well, indicating that the root cause lies within the vehicle’s computer system rather than the alternator itself. Advanced diagnostic tools can help pinpoint whether a computer problem is affecting your alternator’s performance.
3) Wiring Problems
There are lots of wires in the vehicle which deliver power to the alternator. If one of these wires were to become damaged or worn out, then it could cause the alternator to fail at its job and the battery to not get charged.
If you don’t see any of the other problems on this list being present in your vehicle, then check the wiring of the alternator because that may be the reason for the alternator not working.
4) Bad Fuse
Your vehicle’s electrical system contains numerous wires that supply power to and from the alternator. If any of these wires become damaged, frayed, or loose, it can disrupt the alternator’s function, preventing it from properly charging the battery.
If you’ve ruled out other potential causes on this list, it’s worth inspecting the alternator’s wiring. A thorough check of these connections and cables might reveal the root cause of your alternator issues, as wiring problems can often mimic symptoms of alternator failure.
5) Broken Pulley or Belt
Alternators use the mechanical power of a belt and pulley to generate the electrical energy for the vehicle. The problem is that the alternator belt and pulleys due wear out over time.
Pulleys are typically long-lasting but can eventually fail due to age. Belts, being more flexible, are prone to cracking and breaking, especially with prolonged use. If either the pulley or belt fails, the alternator loses its power source, unable to generate the necessary electrical energy.
Here are the additional causes of alternator failure, each described in 50-75 words:
6) Overloading the Electrical System
Adding too many aftermarket electrical accessories can strain your alternator beyond its capacity. Modern vehicles come equipped with alternators sized to handle their stock electrical loads.
When you add power-hungry devices like high-wattage amps, extra lighting, or other electrical upgrades, you’re demanding more output than the alternator was designed to provide. This constant overload can lead to premature wear and eventual failure of the alternator.
7) Fluid Contamination
Engine fluids like oil or coolant can wreak havoc on an alternator if they manage to seep inside. These fluids can damage the internal components, causing short circuits or excessive wear.
Leaks from nearby engine parts, such as valve cover gaskets or water pumps, are often to blame. Regular inspections and simply looking for obvious clues like puddles under your car can help catch these leaks before any alternator damage has a chance to occur.
8) Internal Part Failure
Bearings
The alternator’s rotor spins on bearings, which can (and will) wear out over time. As these bearings deteriorate, they can cause increased friction and heat, which ultimately leads to alternator failure.
Often, you may notice a grinding noise coming from the alternator before it fails completely. Factors like high mileage, extreme temperatures, and constant use in stop-and-go traffic can accelerate bearing wear.
Rectifier or Diode
The rectifier and diodes in an alternator convert the AC current it generates into the DC current your car’s electrical system uses. These components can fail due to heat stress or electrical overload.
When that happens, the alternator may produce insufficient power or inconsistent output, leading to electrical system issues and eventual complete failure of the alternator.
Voltage Regulator
The voltage regulator controls the alternator’s output, making sure it provides the correct voltage to the electrical system and battery. If it malfunctions, it can cause the alternator to under-charge (leading to a dead battery) or over-charge (potentially damaging electrical components).
Modern alternators often have built-in regulators, meaning the entire unit may need replacement if the regulator fails.
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My alternator failed in my 2010 Honda CRV about a month ago and we had to get it replaced. It looks like the replacement one just failed as well. I’m not sure what’s causing them to break, but I think it has something to do with the rattling that can sometimes occur when accelerating. To get the rattling to stop you have to take your foot off the gas for a second. Could this be a belt issue?
Well was told my Alternator blew and it blew the cars motherboard. After ready this I wonder if it might have been the opposite way around. The car was arrived by the dealer two weeks prior just 4 yrs old and had done only 10,100k. I would consider that practically brand new
I meant to write serviced at the dealership
I would be wary of anyone who calls the ECU a motherboard, personally. Maybe they were just trying to make the diagnosis easier to understand, I don’t know.
The pulley and shaft of the alternator on my Volvo XC 70 came out requiring a new alternator. The belt did not break. I had had a new belt fitted (by dealer) three weeks before – could it be that the new belt had been incorrectly tensioned?
I don’t know. I suppose it’s possible, but that sounds like an alternator defect not incorrect belt tension to me. Was it still covered under warranty?
I have a Santa Fe 2007 with automatic transmission, yesterday after a smooth brake I felt something happened in the car and then after a few km the car suddenly stopped fortunately close to the parking place and I just managed with several time use of jump starter get it to the parking. I saw that the tail lights won’t turn off while the car is turned off. Or I can not turn off the front window heating when I start the car with jump starter. it is not a stable electrical system since this happened and the mechanic said change the alternator. It seems that alternator not working but I am almost sure there can be other root causes. Do you have any idea?
If the alternator tested bad, I would start there.
Excessive jump starting can sometimes harm the electrical system of the vehicle. It’s possible the surge from one of the jump starts blew a fuse somewhere.
I have changed 3 new altenator in 4 wks in 2010 dodge avenger what can be my problem
The root cause is probably not the alternator. What led you to change the alternator in the first place?
I am having this issue with dodge avenger also went through 2 alternators in 1 week no idea what this is ? Battery light came in randomly alternator does battery then does replaces both and not 3 days later alternator dies again.
How to do overhauling
Can you please elaborate? I’m not sure what you mean.
I have a 1999vw golf I changed the altnator and it ran good for about 40 mins now what
What were the symptoms that led you to change the alternator?
the altenator is locking up put a brand new one on locked up as soon as i started the car its a jeep cherokee 2007.