How to Diagnose and Replace an Alternator

Here's how to diagnose and replace an alternator on a Mazda 3.

The alternator is responsible for turning the mechanical energy of the internal combustion engine to electrical energy that can charge the battery and power the electrical system in the car. In this video, a Mazda 3 with a defective battery killed the alternator, causing it to die when disconnected from a charger. Once the battery is replaced, the alternator still cannot keep charge.

A multimeter is used to test the battery voltage at idle (14VDC) and under load (12VDC+, with accessories such as the radio, wipers, fan and lights all turned on). A failed alternator would not keep the battery voltage above 12V and therefore cannot charge it. The alternator is accessed under the passenger side front of the engine. Once the belt tension is released, 4 bolts are removed along with two electrical connectors. A teardown and diagnosis of the alternator and its components, such as the voltage regulator, diodes, rotor and electromagnet, stator and bearings follows.

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[davidbaize]

Awesome job!!! I would, as many have already mentioned, would like to see a video on how you removed the broken bolts from the engine block. You always produce excellent, and informative videos 😁👍

[hamentaschen]

Dude, you rock! Thank you for your work on these. Peace!

[michaelbezoski]

Nothing quite like "that feeling" of a bolt snapping. Kudos to you for your professionalism. Me, I would get religious, with a regretful sermons to the "Leader of the Pack", especially when trying to drill square into the centers of the broken bolts, blind. Great job and very good explanation of the alternator's operation. Recommend your channel to anyone I know that wrenches.

[brian]

Bravo my friend.
Excellent info no annoying music straight to the point.
Thank you.

[abdiaspablo]

Thanks for your honesty, some videos from other guys they not honest

[transmitterguy]

You didnt show us the extreme amout of fun you had removing the broken bolts. I bet that was fun. Great videos, can't wait for the next one.

[Mahigeer]

Before removing bolts that maybe rusted, it is a good idea to try to tighten them first. A slight tightening, can break the rust and then a slight loosening and tightening will help keep the cap screw (bolt takes a nut) from breaking. Thanks for posting.

[chrisfreemesser]

No family garments were harmed in the making of this video

[fastfiddler]

Wow... my first two cars were Ford Explorers. 91 and 04. I was always doing something. Did a few alternators. After seeing this, I am glad they were not only mounted topside, but also appear to have meatier bolts holding them on. But... I got my payback in the form of totally seized shock bolts that required a sawzall type of situation.

[anonymous]

One thing my dad taught me, is that idling and putting around work fine for a jump start that day. But put a charger on it in the evening, just to take the load off the alternator. He was a 70s/80s mechanic, but honestly with all the new electronics it's more true.

[MyTreeCrews]

Excellent detail. He waste no time. Learn what you need to know and go 👍👍👍👍👍🛠️

[MeataVore]

Super video as always and my heart went out to you when the bolts snapped on you. Being an ex fitter electrician I understood the gravity of the situation. And having to drill and tap on an aluminum base with steel wedged in, can be problematic at best.

[moonlee]

oh fk. I feel you.That is the worst nightmare when tackling with an old car.

[MrSupernova]

Great video man! Unfortunately, I was stranded once because my car's alternator went out on me. I replaced it myself but being stranded is a real hassle. I recently bought a multi-meter so I can periodically test my alternator the way you showed here. I'm hoping that in the future I can detect the problem before I get stranded. I also have a carbon pile tester and a jump starter for my battery. I hope I don't get stranded again.

[SurferSandman]

This was extremely helpful. Thank you.

[christeschke]

I had a mitsubishi lancer alternator go. Found out they are gold plated when the dealership wanted $1500 for an alternator....good job mitsubishi canada. Ordered one from Mitsubishi japan for $200.

[akudimensional]

I'd like to note that some vehicles may have high output alternators, usually emergency vehicles for all their additional equipment such as light bars and sirens but civilian versions may also have them and one might see a higher voltage than 14v. My vehicle was built as a PPV model and it has one but the car wasn't equipped for police use, instead it has all available trim packages with premium paint and underneath is the wee-woo machine to save money between standard trims and PPV models.

[PCman-]

Great Job! Thanks for taking apart the busted alternator and explaining how it works - especially for mentioning that liquids can get in there, now I think I know what happened with my Mazda5 - btw it looks the same engine-wize as your Mazda3.

[jyao]

Thanks for sharing. Could you tell us how you drilled out the broken studs?

[Enigmaafk]

Or a leaking honda VCM spool valve gasket that will leak right into the alternator :) Gas went up so you can’t afford to run the engine too long :) Nice quick break down.