Diagnosing Alternator Problems - EricTheCarGuy

hello again everybody Eric our guy here and today we are going to be talking about testing an alternator before you replace it so we're going to go through the testing process of finding out if you have a bad alternator or if there's some other issue in the system this episode is also brought to you by BBB industries that remanufacture alternators and starters to meet or exceed OS anyway we're going to start anytime we're talking about the electrical system or doing any kind of electrical diagnosis we always start at the battery so let's head over to the battery do some checks there okay once we locate the battery and some vehicles it may be more difficult than others to try and locate the battery sometimes they're underneath back seats under fender wells all kinds of places that they hide these things on you but once you do find it and you suspect that you have a charging issue or something like that the first thing that I always check for is the condition of the battery connections themselves you want to make sure that the battery connection is clean and tight so many electrical problems actually originate here at connections then also at the battery there's corrosion that builds up over time that creates a resistance between the battery terminal itself and the cable which in turn compromises the performance of not only the battery but the charging system and alternator also so you want it you want to take a look you want to grab the cables and move around and see if they're loose at all and if they're loose obviously tighten them and you also want to check to see if they're if they do have any of that corrosion if they do have that corrosion you want to do what you can to try to clean that up and put that all back together and then make sure you have good connections that the battery before you proceed to the next step in testing something I forgot to mention and that is temperature battery performance is very much dependent upon temperature so whenever you're doing the testing that we're about to show next try to make sure that you're doing the testing between 60 and 100 degrees Fahrenheit so you don't want to do the testing above 100 degrees and you don't want to do it below 60 degrees this will ensure that you're getting an accurate test now I'm going to start by turning my tester on and I want to make sure that my voltage range is on this one I'm going to put it in 20 volts it's not going to exceed 20 volts when I do this testing but then I'm going to take my positive and negative leads and put them on the positive and negative bleeds of the battery I'm getting a strange reading like this there we go you might need to scrape a little bit off of that corrosion and this this goes right back to my point of connections and how important they are because without a good connection you aren't going to get a good reading okay and that's that's pretty much barely good because you want to see reading that's above twelve point four so twelve point four seven is a good reading if you see a reading that's above twelve point six volts the battery is overcharged and you need to remove the surface charge on the battery and there's a couple of different ways you can do that you can either turn the headlights on for a couple minutes or you can crank the engine with the ignition system disabled so that you can take that surface charge off the battery so that you can get an accurate reading but a reading above twelve point four volts is ideal in a situation like this after you remove the surface charge from the battery if there is one you want to make sure to wait a few minutes before you go back and do your testing because you want the system to stabilize a little bit so just give it a couple of minutes after you've either turned on the headlights or crank the engine in order to do that so that you get an accurate reading now that you're sure that your surface charge has been removed and your terminals and all that kind of stuff are clean you're just going to do a general check of the alternative route put to do that you start the engine run at about 1500 rpm and you're looking for a reading of less than fifteen point five volts if it's more than fifteen point five volts that would indicate in overcharging condition which is just as bad as an under charging condition so you want to make sure you don't exceed that there are some systems that may run more but for the most part don't exceed 15 point 5 volts okay that was a good reading now if you go to start this up and run it and you actually have less than battery voltage just from the get-go then you know the alternator may not be putting out but don't condemn the alternator right away go and check those connections at the alternator itself check the wiring check the wiring going to the voltage regulator also for any kind of damage look for any other external cause besides the alternator don't condemn the alternator right away if you do find that condition one more thing to check before you get started is check the belt tensioner if if the belt tension is not sufficient in order to spin the alternator if the alternator doesn't spin it can't produce electricity so you want to make sure that you've got a nice tight belt and that it's it's secured to the pulley and that the pulley doesn't have any any movement in the front of it anything that might cause this not to spin efficiently all right now we're going to have some fun and we're going to load this alternator up a little bit and what we're going to do is we're going to put a load on to the system by turning on everything electrical that we can possibly get our hands on push every button turn everything on rear to foster air conditioning everything that uses up electricity and the in the system and that will pretty much make us so the alternator has to put out as good as it possibly can and we're looking for a reading that's above battery voltage which right now is right around 12.5 so anything that's at least half a volt above that means that the alternator is working if we can exceed that great that means that alternator is awesome and doing a great job I'd say this guy's doing alright now you're asking the really good question Eric what if a voltage it is not above battery voltage by least half of all there are two types of regulators there are external voltage regulators and internal voltage regulators if it is an external voltage regulator recommend replacing that voltage regulator if you find that the voltage falls below specifications there if it's an internal regulator in other words if the regulator is part of the alternator assembly then replace the alternator well actually before you go to replace the alternator once again I can't stress enough how you need to go through and check all those connections and make sure all that stuff is good before you go and replace the alternator but if you find those those connections are clean and tight and the way they're supposed to be then it's it's the alternator is bad and should be replaced on a lot of modern vehicles voltage regulation is also controlled by the ECU and I don't want to rule out the possibility that there could be a problem with the ECU not sending a command of the alternator to put out the proper voltage so keep in mind that that that may be a possibility now that's going to be specific to vehicle so you're going to have to check with the service manual for that vehicle to find out how to check to see if the computer signal is getting to the alternator itself in those instances but just keep in mind that that's another possibility that could step in besides corroded connections or we have something going on with the wiring as something that's not an alternator problem and that's basically why we're going through this we're trying to make it so that you're absolutely sure when you remove that alternator and go ahead and replace it that that is the problem so oftentimes it could be something else so you don't want to just go off and replace things we're going to test them a little bit you know I'm all about that kind of thing something that I thought of when thinking about that computer controlled voltage regulation is you can actually bypass the voltage regulation of an alternator many times and once again this is specific to manufacture in many cases but you do something that's called a full field test to where basically until the alternator to put out as much as it possibly can and if it does change if you've got a situation where a bolt egde regulator is bad in an alternator you can bypass that voltage regulator and just tell the alternator to put out all the time once again that's kind of specific to manufacture but that's another way of eliminating like say a computer control issue or a voltage regulation issue whether it's an external or internal voltage voltage regulator you can take that out of the system so to speak by doing that full field test so for your particular vehicle and an application look into full field testing for for that alternator and do a full field test on it and if you are able to get voltage that's well above battery voltage at that point then you know that the problem is with voltage regulation and not necessarily a problem with the alternator being able to produce electricity lastly we want to completely eliminate the possibility that there's an issue with increased resistance in the circuitry or the conductors in the circuit and we can do this by doing voltage drops on both the positive and negative side of the system so we're going to do a voltage drop on the positive side of the system from the positive output at the back of the alternator to the positive battery cable and we're also going to do one on the grunt ground side from the ground cable to the case of the alternator and see if there's a voltage drop there if we do see it excessive voltage drop there then we know that there's a problem in the circuit not necessarily with the battery or the alternator okay now to check the negative side voltage drop and for that we're going to have to load up the system so you want to go back and you want to turn all of your accessories back on except for the rear window defroster so turn on your AC your wipers your headlights and everything and take one lead and put it on battery negative take the other lead and put it on the case of the alternator and if there's a reading that's greater than 0.1 or 0.2 then there's increased resistance on the ground side of the circuit so I'm going to turn all the accessories on now oh and the other thing is we want to raise the engine rpm up to about 2,000 rpm while we do this test so we connect the positive leads battery negative and the other lead we're going to touch the outside of the case right now there's nothing nothing at all which is a good reading but I still have to raise the RPMs here oh there we go point zero one now we got a reading there of 0.001 volts that's awesome that means there is virtually no resistance in the ground side circuit of the system and actually this this alternator is functioning properly so it's good to know that we're looking at a good system so that if we see something that varies from that now these specifications are from point 1 to point 2 so if you if you see anything point 1 point 2 and above you know that there's a lot of resistance in the ground side of the circuit so you want to go through and check out the grounds like maybe maybe the engine to body ground maybe which those ground straps can break on occasion or the one that goes from the battery down to the engine block itself maybe there's some corrosion there or some damage to the cable something that could cause that increased resistance in the circuit but from what we saw point zero one that's good to go the point of this video is to try to help you out in a situation like say for instance you have a no charging situation and it's actually caused by something external and not the alternator itself so I'm trying to get it to where you can maybe avoid several trips to the parts store taking back where you believe to be a bad alternator something of that nature I can't stress enough about connections and especially connections at the battery and some battery terminals have a tendency to corrode more than others and some terminals that are that are not necessarily factory terminals that are put into place that cable gets a bunch of corrosion on it in that little crimp connection and can create all kinds of electrical problems know starts no charging all that and those voltage drops that we did that will show that so if you have a voltage drop that's greater than those specifications that I gave you either on the positive or negative side you know what side of the circuit you're dealing with and you know where the problem is so definitely don't rule that stuff out also don't forget about those computer controls that could come into play external voltage regulators also can be an issue in fact you're probably more apt to replace a voltage regulator than you are an alternator in many cases at least in my experience but anyway another hearing over there the point is do some de latina due diligence go through your testing figure out what the issue is and if you do have a bad alternator you'll know there will be no question I'm going to stop talking about this and also remind you that this video was in part brought to you by BBB industries that remanufacture starters an alternators to meet or exceed OEM and function i am eric the car guy you can always visit me at eric cargo comm or find me on facebook and twitter and that's about all i can think of for today but anyway take your time do some testing and find out if you really need to replace that part be safe have fun stay dirty take care of people

Channel: EricTheCarGuy

Views: 4,585,078

Rating: 4.7426324 out of 5

Keywords: alternator, alternator diagnosis, charging system, charging system diagnosis, charging, not charging, bad alternator, dead battery, car won't start, no start, no crank, electrical, electrical diagnosis, electrical how to, how to electrical diagnosis, automotive electrical, battery, battery charge, battery not charging, voltage drop, voltage drop test, testing, voltage testing, how to voltage testing, automotive education, diy, diy electrical, eric the car guy, ericthecarguy, etcg

Id: FTGz0PKIl84

Length: 13min 52sec (832 seconds)

Published: Wed Jun 29 2011