Alternators and Alternator Repairs
Car Alternator Photo
Alternators and Alternator Repairs
For most auto consumers, the alternator is an often overlooked, but important part of the car. While the battery in your car is used to crank the ignition and start the car, the alternator’s basic function is to recharge the battery while the motor is running and to power the electrical needs of the automobile. Because the two work in tandem, when one fails, it is often very difficult to diagnose the problem.
Diagnosing Alternator Problems
As your engine spins, the rotors of the alternator producing AC current which is then converted into DC to charge the battery. Even with the GPS running, the alternator should push around 14 volts to the battery - anything under 12 volts would indicate a problem with the alternator. If you have a bad alternator, the car’s battery will never be fully recharged and will simply die like a flashlight that’s been left on all day. Conversely, if the battery is weak or failing , the car’s alternator will constantly run and this shortens the life of the alternator. While manufacturers generally recommend replacing alternators every 75,000 - 100,000 miles - overworked alternators will need to be replaced sooner.
Testing Your Alternator
Using a multimeter set to "Volts DC", touch the red probe of the meter to the positive "+" post and touch the black probe to the negative "-" post of the battery while the engine is running. It should read 13.5 to 14.5 volts. If it is less, the alternator may not be charging. This test is not sufficient though. You may have bad electrical connections to your engine’s alternator - check the wiring to the alternator for frayed or damaged wires. Also check the connections to the alternator to make sure they’re fastened tightly and free of corrosion. Checking the alternator belt is also recommended to ensure that maximum power is being transferred from the engine to the alternator. If you bring your car to a mechanic, make sure they complete all of these tests before you go any further.
Testing Your Alternator’s Wiring
Here is a short list of wiring and fuses to check to troubleshoot your alternator problems. This is not a complete list, but a a guide to the kinds of issues you may be having and where to concentrate your efforts.
- Check the fuse for the main ground cable at the fuse panel.
- Check the field connection wires at the alternator connections with the key turned on.
- If the field wire does not have voltage, check the wire and connectors running between the alternator and the fuse panel for interruptions.
Once you have done these basic tests, you will have a much better idea if your battery has failed, whether the wiring or the connections are faulty, or if the engine’s alternator needs to be replaced.
A Word of Caution
It is a popular misconception that you should test the alternator by removing the positive cable from the battery while the car is running. Although some believe this is harmless enough, manufacturers and automotive makers alike discourage this because doing so can cause explosion, leakage or serious damage to the electrical system of your car or, more importantly and costlier, to the CPU that manages your engine.
Estimating Alternator Repair Costs
The simple formula with all automotive repairs is labor + parts. Rebuilt alternators tend to be more expensive than used alternators, but the rebuilt alternators come with a warranty. You could probably find a used alternator for $50-75 while a rebuilt alternator starts around $140 and up depending on the make and model of your automobile.
More difficult to pin down are the labor costs. Neither the time it takes to do the repair nor the process required for each particular model is the same. It is generally considered that the more complicated the engine, e.g., overhead cams and turbos and the smaller the engine frame and the engine compartment, the longer this kind of repair will take. A mechanics’ time to remove the alternator and replace the alternator can vary from 2-3 hours to as much as 12 hours.
The Straight Scoop on Alternator Repairs
Most shops will build their estimates for an alternator repair based on what the manufacturer’s service manual lists for labor to change alternators. If a shop’s technician can do the job in half of what the manual states, the shop usually will still charge you the “going rate for alternator repair.” In some states, where automotive repair labor costs $50-80 an hour, it’s good to know what the shops’ reputation for this kind of repair is and whether they have mechanics who are experienced with your make and model.
If you are taking your car to a mechanic, you should always ask them to:
- State the amount of hours the service manual outlines for this kind of repair on your car.
- Ask them to be thorough in their testing of all wiring and fuses before replacing the alternator.
- Make sure up front that you know whether the old alternator is being replaced with a new alternator, a rebuilt alternator, or a used alternator - it may make a difference.
- Always have them guarantee their work in writing and put your broken/damaged parts in a box for you.
Using this article to do some of the testing yourself can help you avoid being preyed upon by unscrupulous garages and their mechanics. Making sure you know everything about the repair itself will help make you a better customer.
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