How to Test Your Alternator

Having your alternator fail can leave you stranded on the side of the road. Though it is not necessary to know every aspect as to how the alternator works, knowing a few easy tests and some initial signs of failure can keep you from having a costly breakdown. To test your alternator, follow these simple steps.

How to test your alternator

  1. Gather your materials - You will first need the following: Rubber hose (Approximately three feet), Safety glasses, Voltage meter or digital multimeter, Wheel Chocks

    Warning: When working under the hood with the engine running you want to always exercise caution around moving parts. Make sure that you do not have any loose clothing that can get caught in the engine.

  2. Park car on level ground - Make sure that your car is parked on a level surface if possible and switch the engine off.

    chocks around rear tires

  3. Apply the wheel chocks - Place the wheel chocks around the driver side rear tire.

    car parked with hood open

  4. Open the hood.

    alternator being pointed out

  5. Locate the alternator - On most vehicles the alternator is located near the top, front of the engine. On other vehicles it can be buried towards the bottom making it more difficult to get to.

    belt between engine showing movement

  6. Check the engine drive belt - Inspect the engine drive belt for tightness.

    Tip: Press on the belt between any two pulleys and make sure that there is not much movement. A loose belt can cause the alternator to not charge properly.

  7. Listen for noises - Start the engine and listen for any strange noises such as squeaking or grinding.

  8. Check the alternator's bearings - Place one end of the rubber hose on the alternator case and the other end to your ear. This works like a doctors stethoscope.

    Tip: If the grinding or squeaking is very loud listening through the hose then you may have a bearing failure beginning in the alternator so it will need to be replaced.

  9. Begin testing the alternator - Now you are ready to begin the actual testing. First turn the engine off.

  10. Connect the voltage meter - Turn your voltage meter on and set it to DC volts, place the positive lead to the positive (+) terminal on the battery and the negative (-) lead to the negative terminal on the battery.

    Tip: If the battery terminals are loose or corroded you want to address that issue first.

    voltage meter reading 12.65 volts

  11. Observe the battery voltage - It should read 12.5-12.65 volts.

    Tip: If the battery is low you may want to have it load tested.

  12. Read the voltage on the meter - Start the engine and observe the voltage on the meter. The voltage should read a minimum of 13 volts. A good alternator should put out between **13.5-14.5 volts.

  13. Stress test the alternator - Place a load on the alternator by turning on the headlights, the radio and the air conditioning. The voltage should remain high with these circuits on. If the voltage does not change when the engine is started, if it does not get above 13 volts, or if it charges above 15 volts then the alternator may be faulty.

    Tip: If the voltage is low, you can lightly wiggle the electrical connections on the back of the alternator to see if the voltage changes. If it does then it may just be a bad connection. Loose or corroded connections on the alternator or the battery can cause bad alternator readings.

These tests are a good way for you prevent sudden breakdowns.

If your tests do not result in any problems, but you continually get a battery warning on the dash of the vehicle, have issues with dead batteries, further testing is needed.

If are not comfortable performing these steps, you should enlist the help of a certified mechanic, that can test or replace your alternator for you.


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Recent Alternator Repair reviews

Excellent Rating

(7,113)

Rating Summary
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217
43
29
102
6,722
217
43
29
102

Attila

19 years of experience
906 reviews
Attila
19 years of experience
Infiniti G37 V6-3.7L - Alternator - Basking Ridge, New Jersey
He was faced with a difficult situation due to unexpected rusted bolts, poor access, etc. but he got the job done on time and on budget.
Honda Accord - Alternator - Scotch Plains, New Jersey
Mr. Paniti was punctual and very professional. He kept me up to date on what was going on. He had to go pick up the right alternator, he called me and informed me of the situation. The car started and he made some recommendations. Great service Thanks

Collins

12 years of experience
488 reviews
Collins
12 years of experience
Acura RL V6-3.5L - Alternator Repair - Atlanta, Georgia
Collins is a true professional. Arrived on time and answered all of my questions. I would use him again.
Nissan Altima - Alternator - Atlanta, Georgia
Collins was incredibly kind, professional, and went above and beyond to get my car running. So thankful to God of all the mechanics that I was blessed with him. ❤️❤️❤️ Thank you 

Thomas

12 years of experience
96 reviews
Thomas
12 years of experience
Jeep Patriot L4-2.4L - Alternator Repair - Grand Prairie, Texas
First time using your mechanic app and Thomas was great! Attentive, kind, and professional. Made sure everything was good to go before leaving.
Honda Civic - Alternator - Fort Worth, Texas
Thomas was very knowledgeable in both mechanical and electrical issues with my car. He was great with explanation of the issue, as well as making the repairs to my car efficiently. I highly recommend him as a mobile mechanic to anyone I know!

Robert

20 years of experience
1089 reviews
Robert
20 years of experience
Mercedes-Benz C300 V6-3.0L - Alternator - Thornton, Colorado
Was on time and completed the job to my satisfaction. Will use again when any of my cars or trucks needs work done to them. Thank you.
Toyota FJ Cruiser - Alternator - Westminster, Colorado
Robert is a great mechanic, and I will definitely be looking to use him for further work. I used to troubleshoot and work on cars, but I lack the expertise to tackle modern electrical systems. Robert efficiently diagnosed the problem, and fixed the car within the estimated timeframe.

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