How to Test an Alternator

Hey Chris, I'm a retired auto mechanic, with 4 years experience at General Motors Assy Division, (Back from 1978--1981), then 15 years as ASE cert master at a Chevrolet Dealer, then 4 years at an automotive mechanical claims facility (Call center for under 800.00 repairs). I have to thank and congratulate you for the outstanding job you're doing. You are helping people and asking nothing in return but for people to subscribe to your channel. You are helping thousands of people from being fleeced by the people that take advantage of people that don't know anything about the automobile or the industry that's giving them a bad name due to greed and corruption. My guess is the thumbs down people are the ones losing money thanks to your YouTube help. I just want to thank you and salute your help to people that are tired of being screwed by the shops and mechanics that are more concerned with making money than keeping customers happy.

Outstanding video. Shady mechanic told me I had a bad alternator. Ran these test and it was within the mentioned volt range. All that was needed was to clean connector to alternator. You saved me $350. THANK YOU!!!!

You are my hero. Since I lost my husband I've had to figure out how to do a lot of things on my own. The information you provide is detailed and specific and clear and anytime I watch one of your videos I come away with confidence that I have learned what I need to know from you. I appreciate so much everything you post because even if it doesn't apply to me today at some point I'm sure I'll need the information and the information you provide is so good thank you so very much for everything you do.

I really enjoy your tips and this one saved me a ton! Our 6 year old Lexus had trouble starting so I took it to Lexus. They said I needed a new battery ($400) and a new alternator ($600). They charged me $120 to diagnose! I guess I should have just gone to an auto store! Looking at the battery I noticed it was the original and there was a label indicating an 84 month warranty. I asked the service advisor and then he told me that I was eligible for a 25% proration off a new battery so it would be “only” $300 but he highly recommend terminal cleaning and protection for an additional $25. I was pissed so I paid the $120 diagnostic fee and drove it home. I went to Costco and bought a larger AGM battery (27F vs 24F) and it fits perfect. I then followed your steps and discovered that the alternator is fine. I could kick myself for taking it to the dealer for diagnostics but I didn’t know how to check the alternator until later. Thanks and keep up the great work!

Finally, someone that do an instructional video that's to the point and no rambling about irrelevant matters unrelated to what the viewers are seeking. Chris you are the textbook example of how videos for DIY's should be done. Thank you much.

Man, Life would have been easier 50 years ago if we had the internet. Life is getting better in a lot of ways. Not all though. Thanks, and you deserve your subscription and view numbers.

It's been a while since I've had to test an alternator so I needed a "refresher course". I'm glad to have found this simple, too the point video that told me everything I needed to know. It helped me figure out that my brothers car didn't need an alternator but just a new battery. We had several days of sub-zero temps last week and his battery gave up. Now, if I can only get him to reimburse me for the price of the new battery lol!

Chris, you are a ROCKSTAR! Thank you for helping me fix pretty much every issue I have had with my vehicles. You’ve helped me save $1000’s of dollars doing it myself! Thanks man!

Thanks for an elegant, good, informative, clear, uncluttered video. I didn't have to sift through bad comedy or bad music or other gimmicks but just got what I needed. Well done and thanks again.

Just saved me $150! Cleaned connection to alternator and now it is working like new!

Can’t thank you enough. You helped me determine that my alternator was, in fact, bad but more importantly when it came time for me to replace it I paid extra close attention to the wires and bolts only to find that my negative terminal on the battery was rusty, the chassis ground was loose, AND the chassis ground wire was frayed. As soon as I replaced the alternator and negative terminal wiring my car started right up and it sounds better than ever. Thank you so much.

Love your videos Chrisfix! I used this video to diagnose an alternator issue with my 2008 Civic. It's almost at 300000 kms and your detailed and thorough videos are a big part of helping it make it to that milestone!

One of the best auto DIY videos I’ve watched. Easy to follow, explained well without over doing it. Extremely helpful- thanks.

Hi your video is really GREAT! The way you do this voltage drop tests make a lot of sense! I am a retired electric engineer, with more than 50 Years of experience and I never saw this very logic tests IN A CAR! Keep on going my friend!!!!

1989 Jeep YJ owner here. Thanks Chris for this very well explained video and giving me clear instructions on how to check all this and the reasons and logic in strange readings. Brilliant video. Thanks for reaching me how to figure these gremlins out and what to clean and replace. 100/100

Terrific video. To the point with no useless commentary. Thank you so much for the great detail in what to do. 👍🏻

Thank you, young man. You really packed in a whole lot of information. Great job. A video cleaning the connections would be helpful. Not for me, but for those new DIY'S out there. A lot of money is wasted on buying alternators and batteries that are not needed. Happy New Year and have a blessed 2020.

I was always told to disconnect the positive cable from the battery and if the car shut off, it was the alternator. I just checked everything like you described, and it turns out that it is the alternator not producing enough current. I'm still going to use your tips, especially after I install the new one. Thanks for your tips on properly diagnosing an alternator, I'm sure you've saved a lot of people a small fortune.

Well explained, and I love it when you say, "I'm good." Then move right along... very informative and efficient. I test wires in the field for a living, and I learned a few tricks to apply to cars. Great job, and you have a subscriber. You know your stuff.

Chris keep up the great videos. You teach me more about auto maintenance than anyone else on Youtube.