The two roles of the alternator are to recharge the vehicle’s battery once the engine is started and to meet all of the electrical demands during vehicle operation. It does the latter by converting some of the engine’s rotating force into electrical current taken off through the accessory belt.
Signs that an alternator might need to be replaced are: system voltage is low – particularly with a lot of accessories on, the battery warning light is on, or the battery is discharged. If a vehicle starts slow or has a dead battery, it’s a normal thing to have a charging system check done which tests the battery and the alternator to see which one is the problem.
Typically, this is about a quarter-hour labor charge; $15 to $25 in most places. Many parts stores are also able to test batteries and alternators often at no charge.
Costs of Alternator Replacement
Most alternators are easily accessed, being typically on the side of the engine near the top. They generate heat as they work and they are usually put in a position where they have good airflow.
This leads to a common labor time for replacement of about an hour, though, there are a few vehicles where significantly more time is needed. Most often, labor on an alternator replacement is billed at book time.
Parts costs can vary widely. A typical aftermarket alternator, new or remanufactured, can vary from $150 to $300. New OE alternators through a dealership range from $400 to $600 on average.
For some specific alternator repair cost examples, assuming a $100 per hour labor rate:
- A 2010 Toyota Camry with a 2.5-liter engine: $210 for a remanufactured Denso alternator and $675 for an OE Toyota alternator. With an hour of labor, the total cost would be $310 using Denso and $775 for the OE.
- A 2011 Dodge Journey with a 3.6-liter engine: $275 for a remanufactured Mopar alternator and $507 for a new Mopar part. With 1.4 hours of labor (“book” time), the total cost would be $414 for the remanufactured part vs. $657 for new, installed.
- For a 2010 Chevrolet 1500 truck: a new AC Delco alternator is $225 and a new OE alternator through the dealer is $569. The total cost to replace alternator with 0.6 hours of labor would be $285 for the AC Delco and $629 for the OE.
Remanufactured vs. New
Most shops would recommend a new alternator as they have the best reliability. However, depending on the vehicle, there is usually an abundance of remanufactured alternators available while the new ones can be harder to source.
On the common models, the prices are often pretty close for either type, while on others, there can be a significant price difference. As long as a good warranty is available, a remanufactured alternator can be a good choice.
Remanufacturing thoroughness varies. Most of the time though, there is a good chance that a remanufactured alternator will last as long as a new one.
Common Alternator Failures
Fortunately, alternators are fairly easy to diagnose. They are designed to keep the voltage of the vehicle within a certain range under all loads. Testing the voltage and the voltage under load is a simple way to verify whether the alternator is working or not.
Of course, all the normal things with an electrical diagnosis should be done during a test. The battery should be charged, connections verified, and the fuses related to the charging system (if any) checked.
The basic wearing part on an alternator is the brushes. These will slowly wear through use and eventually, begin to lose contact.
When this happens, alternator output and system voltage drop. Most vehicles have a battery light that will come on when the alternator output drops below the level that allows keeps the battery charged.
There has long been some controversy in the repair industry as to why this light displays a battery rather than an alternator. Perhaps the best explanation is that an alternator is harder to depict.
Alternators can gradually lose output capacity and early signs of failure include a vehicle with all loads on (lights, AC, blower, etc) will sometimes have a problem with dimming lights. They can have low voltage if there is a volts gauge on the instrument cluster. They can also go out suddenly if the voltage regulator or internal circuits that feed the voltage regulator fail.
Another less common problem is diodes failing which are built into the alternator. Diodes convert the AC current the alternator produces into the DC current that the vehicle uses.
If one fails, then, the current supplied isn’t smooth DC current but partially AC current. This can cause a variety of unusual electrical issues but it’s also easily diagnosed.
A diode is also like a one-way valve in the electrical system; on rare occasions, they fail in a way that bleeds current back through the system and can discharge the battery.
Other Things to Consider When Replacing the Alternator
In order to replace the alternator, the serpentine belt must be removed. If there are any indications that the belt should be replaced (if it’s showing cracks, if the rubber is old and hard, etc), then, this is a good time.
A failing alternator can discharge the vehicle battery. If a battery is in marginal condition, recharging can place a lot of stress on it and it might not be reliable.
A new alternator has to work harder to keep a marginal battery in shape and this can place it under unwanted stress. It’s common, when in doubt, that a new battery would be recommended along with an alternator replacement. If that isn’t done, it’s best that the battery should be fully charged before a new alternator is installed.
On rare occasions, wiring problems can prevent the normal operation of an alternator. Diagnosis of wiring faults is usually done at an hourly rate and it’s not usually possible to say in advance how long it might take to diagnose and repair a wiring issue.
On newer vehicles, a dealership would have an advantage. This is due to having the best access to wiring diagrams, diagnostic procedures, and proprietary software that allow access to all the necessary module data and functions.