Alternator Causing Parasitic Drain

Have you performed a parasitic drain test with every possible fuse removed yet still get a high amperage draw? Check the alternator! It has a direct feed and depends on a series of diodes to keep voltage from draining from the battery when the car is off.

[DJDevon]

Update: His MX-6 is back to normal after replacing the alternator.

[TwinShards]

Thank you for this old but relevant video! Within a few months my mom's car alternator started dying and went completely dead. We repaired the alternator at a shop and i've been seeing Amp draw of over 5A while the car is off. Time to check this out!

[jessicaulmer]

Other video makers take note! That's the way a video should be done. Great work guys. Most of us would not be watching this if we needed to be schooled on which tools, safety, blah blah blah. Most of us are seeking straight forward ideas we haven't yet thought of, the clear facts with completeness and you guys set the bar for the way these should be done. Excellent! I've watched 1000 videos and this is my first public comment.

[dluxdiy]

You guys know your stuff. Thanks for the video. I'm in the middle of troubleshooting a parasitic draw on my '06 MDX. I was scratching my head a bit after pulling all my fuses and getting minimal drop. This video gives me a few things to try next as I track down my issue.

[DJDevon]

The alternator produces AC voltage which is converted to DC by the diode rectifier. This is why it's named as "alternator" because prior to the diodes it's actually producing alternating current. Depending on how many diodes fail will depend on if your 100A main fuse will blow or not. Some people with this specific problem may OR may not have their 100A fuse blow depending on how many diodes in the rectifier assembly fail (and in which order). There is usually an unknown variable in this equation, which is the order and number of diodes blown in your AC to DC rectifier. Makes more sense now? Andy got lucky as it was still producing some DC voltage under load, enough to get him home, however the diode that prevented voltage/current draining to ground was blown. I'll say this one more time to make it crystal clear, for the Mazda 626/MX6 a diode rectifier is almost as expensive as a new alternator because they normally come as a set. That is not true of all vehicles but it is of the Mazda 626/MX6. The alternator uses the engine block as its ground on this vehicle.

[pepoppa]

Great fkn diagnosing job! If I see a couple more jobs from you like this, I will definitely become a subscriber.

[renewcrew]

Theres an oil leak around here * motions the entire engine hahah

[smartdummy]

By "jumpered" DJ means that he is basically bypassing the 100amp main so he can trace the draw to the external electrical system (alternator, starter, etc.).
You can do this with a wire hooked up from one terminal to the other. Just make sure it can handle 100amps or more for safety. Then you proceed with the standard parasitic draw test.

[ahmedissa]

Great information, I have been experiencing battery drain every morning.

[smwodjz]

Cant we just put a big diode on that feed positive cable?

[carnut]

Haha, your friends description of the oil leak was very funny because I can totally relate. My current 626 leaks oil 'everywhere' too.

[stuzman]

Nice diagnosis DJ. You can do a quick check on the six diodes without taking the generator apart. Your diagnosis implies there is a shorted diode(s), but this test will confirm it. Take the battery wire off of the generator. Then set your DVOM to diode check. Place one lead of your meter on the B+ stud of the generator and the other lead on the generator case. You should get a voltage reading of about 1.5V (approx.) or OL. Reverse the leads and your reading should reverse. In other words, it will check just like one diode, although you're checking all six diodes in one swoop. You will probably see that the voltage readings are very low in both directions indicating shorted diode(s). Here's one of Richard's videos of where he demonstrates the process.
Alternator Check
Take care DJ...

[punktrixter]

Mate thanks so much for this video, I've been over my fuse's like ten time's then found this video and cured the problem. Cheers.

[anthonywilson]

Awesome. Exactly what I am experiencing. Was frustrated tracing the issue and came the same conclusion. Thanks for posting. Helped to verify my issue. I also get a random misfire on hard acceleration, performance loss, stalling and voltage drop to around 9-20 bolts at high rpm. Comes back to normal 14 when rims drop. Diode in alternator pretty sure.

[thehamburglarmm]

Chek for AC voltage between battery posts when engine is running. this indicates a bad diode in the voltage rectifier that is not blocking out half of the AC wave created.
I just replaced the rectifier in my truck.

[Schenevey]

Great video, very educational! Thanks for your effort.

[littletoze]

Great video! Thanks for the input. I watched it again to see how you hooked it up. it's a "Rectifying Diode". Converts Ac voltage to a DC. "kinda" ;)

[MWARIS]

Great work Dj on finding out the issue, I remember testing my battery even though I had bad battery I was still getting 14.02V on Idle, but really I had problem like this, it would be impossible for me to find because most of the time I work alone in my cars, Damn I wish you guys were near me :D

[smartdummy]

I think DJ means that you're suppose to disconnect both battery terminals before you remove a fuse or alternator terminal. That way you don't fry something as you're taking off the component. If you were to touch metal or something.
And once the component is off and isolated you connect the positive (red) wire back to test for a draw.

[ronaldlincoln]

Call me lazy, but I had an intermittent parasitic draw on my brand new battery and it kept draining out like with you. I did some basic testing and instead of doing all the work you had to go through I figured since it was cheap enough and because my alternator was really old anyway, that I would just switch it out for a new one and see if it fixed the problem. It did. I guess I am lucky like that! Also, keep in mind that a dying alternator can actually work and not work intermittently for years. You can do all the alternator tests in the world and find that the alternator tests just fine....only for it to fail on you two days later. You have to test multiple times over a period of days to catch that sucker not working.