How to Test an Alternator Diagnose Easily Yourself

hey guys welcome to ask my auto mechanics so in this video we're going to be testing an alternator to see if this car here has a bad alternator [Music] you're going to find this video helpful if you're having a problem with your car and you suspect the alternator might be going out it doesn't charge me your battery properly what I'm going to do is show you guys how to test that to see if your alternator maybe your problem on your vehicle now if you're looking for a video on how to change an alternator this is not really it I'll give you a couple tips in this video but this is mainly how to test to see if your alternator is bad alright guys so one of the first things you want to do when checking the alternator on your vehicle is to make sure that you have your battery tested before you do it now make sure that your battery is completely charged and or replaced before you test the output of your alternator and then another thing you want to do to make sure your alternator is getting the power that it needs make sure you check all the fuses so on this little Civic here you've got a fuse box right next to the battery inside there is going to be different fuses you also have fuses underneath the dash in the fuse box in there make sure you locate the correct fuse for the alternator turn the ignition on without starting it and check that fuse one way to do that is with a test bike now test lights are really simple in that you can check fuses really easily what you do is you put this little tip on the one side of the fuse the little metal part and then you stick it on the other side and if you get the light to light up like if I take this fuse here this little 10 amp fuse you can see I've got it on one side and the light is lit up there and then if I go to the other side and check it if the light lights up I know that that fuse is good if it didn't light up on the other side it only lights up on on one side that means that the fuse is bad you want to replace it so check your battery have that tested at a park store or something like that make sure it's charged check your alternator charging fuse to make sure that that is a fuze there all right guys so to test the output of the alternator what we're going to do is we're going to use this voltmeter here you don't need a high-dollar voltmeter just a voltmeter to test the volts at the battery again make sure your battery is fully charged before you do this and then go ahead and start the car and put these two terminals on here on the battery and then check the voltage output right at the battery all right guys so you can see I've got the voltmeter hooked up to the battery here now the engines not running and we're running at twelve point three three volts there without the car started now once you start the car the alternator is supposed to kick in and run this battery up to about fourteen point four volts depending on if your headlights are on and things like that it's always best when you're checking the alternator to go ahead and turn the headlights on when starting the engine to give it a little bit of a load to see what the voltage reads at now if you're reading somewhere between about thirteen and a half and fourteen fourteen point four volts then the alternator is most likely just finding is giving the battery plenty of volts to recharge it alright guys so what we're going to do here is we're going to start the engine and see if the bolts comes up I'm gonna turn the headlights on I'm gonna start it and see what kind of voltage the alternator is actually pushing out alright guys I've got the headlights onto the car and got this thing starting and running we're actually running about eleven point nine for eleven point nine five volts so the cars electrical system is actually pulling more volts off the battery the alternator is definitely not giving any extra charge to the battery they keep it running alright so we know that the alternator is not pushing anything out now what we don't know is the alternator being commanded to turn on so this is a new alternator I've already tested this car I know that the alternator is bad so I already picked one of these up and basically they're fairly simple to install once you get to them it just has two main bolts on this model that hold it in place some of them have three or four bolts to hold them in place and then you'll notice it has this positive terminal here so this is what they consider the charged wire post and what you have is a fairly big battery cable that comes off the end of this post and this sends the electricity out to the battery to charge it so you want to take your multimeter and check the charge output right here rather than just at the battery after you've checked at the battery you want to locate where the alternator is and carefully check the power output when it's running if you've got 14 volts coming out of the alternator but you don't have to have that voltage at the battery that means you have a problem between the alternator and the battery the cable or something has got some resistance in it so you do want to check the output right from the alternator the other thing that you want to do is check these pins here so there is an electrical connector that plugs into the back of this and one of the wires commands this thing to actually turn on there's actually a couple there that tell this thing to charge if the alternator is not receiving this signal to tell it to charge then it won't turn on and won't put any output on it there's also wires that come out of it to go to the the lights and the - to give the battery voltage to the - a little gauge or light indicator whatever that's there but the main thing you've got to determine is this thing being told to charge so you've got to test the wire that tells it to charge okay to test the wire that is going to the alternator to make it charge what I've done here is I've taken a test light and you can see this orange wire that I've tapped to the back of the alternator now this orange wire is not normally there it's just there to show you guys that this wire is sending power to the back of the alternator from the car now I've just taken a little tea tap there and tapped on to the factory wire and ran the orange wire up and over to the test light just to show you guys that it's actually getting power when the car is running and it's turned on okay so we have the car running let's check to see the computer is sending the alternator the voltage to turn it on okay yeah so you can see that this test light here is lighting up that means that this wire that's telling the alternator to turn on is getting the signal and it's lighting up our test light however if you look at the multimeter here we've only got eleven point nine five volts which means the alternator is not putting power to the battery and the alternator is definitely bad alright so we know that our alternator is bad it's not charging the battery so we need to change this thing and then once I changed the alternator I'll retest the output right there at the battery to make sure we're getting the proper charge voltage when we're all done alright guys so this is not really a video on how to change the alternator but more to test it however now I'm gonna go through and change the alternator basically take off the alternator drive belt undo all the connections to the all-rounder make sure you disconnect the battery first before you start this repair and then take the belt off undo all the connections unbolt the alternator put the alternator back on tighten up the belt reinstall the belt and tighten it up hook your battery back up and then check to see if we've got charged voltage so let's get after this so I'll put it on a quick little maybe gopro timelapse of changing the alternator and we'll get this done I finally got a stupid thing out so much fun if you're working on this 99 Honda Civic model like I am don't bother trying to pull it alternator up through the top this would be much easier to do if you have choice so go ahead and raise the vehicle up off the ground with jack stands and pull it out through the bottom but make sure you take the bracket that holds the bottom of the alternator out and that'll make this come right out of the fender world alright guys so we've got this thing all finished up got the alternator all bolt it back up the belts adjusted I've got all the electrical connectors hooked up so we'll go ahead and hook up the battery and retest it with the multimeter to see what kind of voltage were getting out of the charging system alright guys moment of truth here we've got the multimeter hooked up to the battery we've got twelve point three seven volts let's see what kind of voltage we get now that we've got the new alternator on the car firing this video [Music] [Applause] all right yeah so generally I deal out of an alternator is fourteen point four volts so there you have it we weren't charging before we change the alternator we're charging now all right guys thanks for watching ask my own mechanic I hope you found this video useful and they covet it go ahead and hit that like button if it did subscribe to my channel for more auto mechanic related type questions and tips also if you're looking for more how-to type videos I have another youtube channel DIY Bry go ahead and check that out I'll put that in the link below or somewhere at the end of the video also any tools that I might use throughout my projects or in my videos I'll put those in links below the video so make sure you check out that along with other helpful tips [Music]

Channel: Ask My Auto Mechanic

Views: 610,185

Keywords: Diagnosing Alternator Problems, how to test an alternator, how to test alternator voltage output, how to test voltage drop, how to test a failed battery, car battery test, car battery not charging, checking alternator, how to check an alternator, checking a charging system, lights dim, slow start, no start, alternator output, how to car repair, diy auto repair, battery dead car, car clicks but wont start, How to Diagnose a No Crank No Start, test alternator yourself

Id: ZGwmOd8KvyQ

Length: 10min 47sec (647 seconds)

Published: Tue Oct 31 2017