Possible alternator problem?

2001 HONDA CIVIC
236,000 MILES • 1.7L • 2WD • AUTOMATIC
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CJC719
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I woke up one morning and went to start my car and it just gave me the ol clicking noise. So I took the battery to O'reillys and they checked my battery and charged it. The battery read good and my car was running again but something still seemed off. So I took it to AutoZone and their test said the battery was bad. I finally decided to just go out and get a new battery and a multimeter. The new battery read goods when the engine is off and around 13.6 with it on. I noticed when I put the A/C on it drops to about 12.4. Also when driving for a while it seems to drop slightly too.do you think it could be alternator instead? I'm just wondering why it tested good at AutoZone under load? My regular mechanic checked it out a couple months ago too, because my battery lights been on since I purchased it and he said alternator was good to? He said battery light was just needing to be reset.
Jul 17, 2021 at 11:33 PM
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ASEMASTER6371
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Good morning,

You have a charging system issue with the alternator. The voltage should be 14 to 14.5 volts at the battery with the engine running.

https://www.2carpros.com/articles/how-to-check-a-car-alternator

https://www.2carpros.com/articles/how-to-check-wiring

13.6 is no good. It sounds like you have a bad diode in the alternator. You should replace the alternator.

https://www.2carpros.com/articles/how-to-replace-an-alternator

As far as the battery, many people test batteries in different ways. It can test well today and fail tomorrow.

https://www.2carpros.com/articles/car-battery-load-test

Roy
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Jul 18, 2021 at 3:48 AM
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CJC719
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Thank you, I really appreciate it. I kind of figured it was the alternator but it's always good to have a professional opinion. Do you think it's something I should even attempt myself being it's probably my first DIY under the hood. I would like to be able to work on my own car eventually. But I just don't know if this would be a good place to start?
Jul 18, 2021 at 11:57 PM
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ASEMASTER6371
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I think you can do it, just take your time. Follow the instructions and make sure you put back everything you take apart.

Roy
Jul 19, 2021 at 3:15 AM
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CJC719
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Okay, thank you Roy.
Jul 19, 2021 at 6:51 PM
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ASEMASTER6371
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You are welcome.

Always glad to help.

Roy
Jul 19, 2021 at 6:56 PM
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CJC719
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One last thing; is there any specific tools I need like a belt tensioner? I just have the basics, I know some videos are saying I need a jack stand but all I have is the basic jack the car comes with?
Jul 20, 2021 at 11:12 PM
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ASEMASTER6371
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No, basic tools are all you need for this repair.

A standard wrench will release the tensioner for the drive belt.

Roy
Jul 21, 2021 at 1:13 AM
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CJC719
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Is there a way to make sure the belt tension is correct? I know if it's loose it'll squeal or whatever.
Jul 26, 2021 at 6:10 PM
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ASEMASTER6371
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It needs to be taunt. make it tight so there is no deflection in the belt.

Roy
Jul 28, 2021 at 12:20 PM
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CJC719
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Okay, thanks again.
Jul 28, 2021 at 12:45 PM
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CJC719
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So I installed new alternator and the battery light was finally off when I started it, Everything seemed good. I was getting over 14 volts but when I turned the A/C on again it started to fall to about 13.2 and kept dropping like before. I figured maybe it was just because I was in idle. But when I drove it the next day the voltage dropped again but this time while driving. The battery light even shut on again for a few seconds. The belts are good too, nice and tight. I have no idea what's going on?
Aug 2, 2021 at 8:45 PM
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ASEMASTER6371
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I would have the new alternator tested. Remove it and take it back to the parts store and have them test it. It is a free service and they can check it off the car.

Roy
Aug 3, 2021 at 2:53 AM
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CJC719
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Yeah, I did that and they said it was good. It reads fine until I put the A/C on.
Aug 3, 2021 at 2:27 PM
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ASEMASTER6371
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Okay, when you put the A/C on, what does the voltage drop to?

Roy
Aug 3, 2021 at 3:07 PM
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CJC719
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It will keep dropping if I let it. The lowest I seen it go was around 12.4 and I shut the A/C off.
Aug 3, 2021 at 4:22 PM
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ASEMASTER6371
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Is the engine idle correctly? If the engine RPM drops, the charging rate will drop.

Roy
Aug 3, 2021 at 4:24 PM
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CJC719
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Idle seems fine, it happened while driving yesterday. I felt like I was barely going to make it home. Do you think I over tightened the nut that connect the charging wire to alt? Or is it possible to over tighten alternator belt?
Aug 3, 2021 at 4:56 PM
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CJC719
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Disregard that last part because I'm sure it has nothing to do with over tightening or any of the work I done. Because this is the exact problem I had before installation. Also, I wanted let you know I drove around for a few yesterday without A/C and everything was good.
Aug 3, 2021 at 8:23 PM
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ASEMASTER6371
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I still think that the alternator is the issue. It may test okay on the test bench but under load, it may be failing internally since the A/C system does draw a lot of currents to make it work.

Roy
Aug 4, 2021 at 2:28 AM
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CJC719
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So you think the new alternator I bought from AutoZone is possibly bad? I know it happens, it's just crazy how it's the exact problem I had before and all the readings are fine with everything else on brights, radio, hazards, inside lights. It works fine when I put heater on or just the fan too, it's only when A/C kicks on.
Aug 4, 2021 at 1:31 PM
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ASEMASTER6371
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I think it is failing under a load.

Roy
Aug 4, 2021 at 5:12 PM
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CJC719
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Okay, well it's good thing I got a warranty. I will just swap for another and see what happens. Last question, is there anything else that it could possibly be if this doesn't work?
Aug 4, 2021 at 6:04 PM
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ASEMASTER6371
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The alternator is responsible for the charging system. There is nothing else in the circuit.

The only other thing is the ELD unit in the underhood fuse box. It is rare but could cause the issue.

I attached the description and the procedure for you. If it is that, the fuse block has to be replaced.

Roy
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Aug 5, 2021 at 2:31 AM