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Discussion Starter · #1 · (Edited)
Hi folks,
I have a 2015 Honda Civic Si with ~90k miles on it which I bought new. I'm replacing the alternator. We already removed the Denso alternator that was in the vehicle. This is my main vehicle, although I'm not driving it a lot these days at all as I no longer have my usual hour commute to work. I drive it at least 1-3 times a week.

I can buy a remanufactured alternator from NAPA for ~$200 (core already included) which comes with a limited lifetime warranty OR I can buy a used original Denso alternator (same one) for ~$100 (core already included) from a junkyard which comes with a 6 month warranty. Any suggestions? Is it a bad idea to buy a used original alternator from a junkyard? I plan to keep this car long term.

Side note, originally my car wasn't turning on so we first took the battery to get tested at Advance Auto parts (it is fairly new, purchased in May of 2020). I was told the battery tested good. I put it back in the car and was able to turn the car on. When we tested the voltage with the car on (no significant load, just turned the car on), the voltage was around 12.2-12.4. We would have expected it to be higher around 13 or 14 volts with no load. Now, I'm not sure if that may have to do with the fact that newer civics seem to have a battery sensor connected to the terminal which make the alternator more efficient. So, not sure if the battery sensor might be playing into this or if the electronic load detector may be playing in this, which is the brown box in the fuse box under the hood.

We sort of jumped ahead an removed the alternator before looking into the battery sensor or ELD because of the low voltage when the car was turned on. My dad had linked a basic battery/alternator tester to the battery which indicated the alternator wasn't working (again not sure if that has anything to do with the newer generations having a battery sensor now).

So, since we took the alternator off, we took it to Advance Auto parts, Pep Boys and Auto Zone, but they weren't able to test the alternator. It seems as though for some reason it isn't compatible with their testing system.

Any suggestions on remanufactured vs used OEM from junkyard alternator are greatly appreciated! Also, any thoughts on battery sensor or ELD as well as any other shop that might be able to test the alternator off the vehicle in NJ.

Thanks!
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my civic does the same thing with keeping the running voltage low. honda probably does that to protect some system components. If the battery is testing good then there's not reason to believe the alternator isn't working right?
 

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Discussion Starter · #3 ·
my civic does the same thing with keeping the running voltage low. honda probably does that to protect some system components. If the battery is testing good then there's not reason to believe the alternator isn't working right?
Not sure, we sort of jumped ahead and assumed it was the alternator because after confirming the battery was good at advance auto parts (it had low voltage and they charged it for me) we put it back on the car, turned on the car and used a simple tool that connects to the battery that indicates if battery/alternator are good. It showed a good battery as expected, but showed a bad alternator. We tested with a voltage meter and saw the reading hovering around 12.4 with no load and car on. We assumed it was the alternator (at that moment didn't consider the battery sensor or eld) so we took it off to get it tested because I was worried I might get stuck somewhere with the car if we decided to drive it. Turns out pep boys, auto zone and advance auto parts can't test the alternator. Now we're wondering if it may or may not be bad but the only way to truly confirm would be putting it back on the car and seeing if the car turns on and potentially drive it advance auto parts so they can test while on the vehicle. Or assume it is bad and replace it. 🤷‍♀️
 

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here's the thing, how the alternator charges the battery is completely different from how a dedicated unit charges a battery. I would assume your alternator is good. if the alternator was bad you would more than likely have a constant battery light indicator on your dash.
happened when the alternator bit the dust on my Pilot back in 2019 literally a month after I bought it.
 

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Discussion Starter · #5 ·
here's the thing, how the alternator charges the battery is completely different from how a dedicated unit charges a battery. I would assume your alternator is good. if the alternator was bad you would more than likely have a constant battery light indicator on your dash.
happened when the alternator bit the dust on my Pilot back in 2019 literally a month after I bought it.
That's my dilemma. When the car did turn on after the battery was put back in, I didn't notice any strange dashboard lights or any sort of message. Do you think the car obd2 might provide some sort of error code for the alternator or a part of the charging system if there is in fact an issue at all? I was considering getting the Innova scanner that includes charging system errors... hoping that portion of the scanner would be compatible with my car.

Background info, when the car first wouldn't turn on, we tried jump starting the battery, but that didn't work... that's when we decided to get the battery out and checked at advance auto parts but turned out to be good just low so they charged it. Which it should be good because I bought it in May of 2020 to replace the original battery which died.

The upside is I don't necessarily have an urgency to get the car fixed right away and rather than spending money on another alternator without knowing if the current one even has problem at all it might be better for my dad and I to put it back in, turn on the car, check for dashboard lights and take it from there.
 

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Discussion Starter · #6 ·
Update: car is running... we put the same alternator back in...we took it to advance auto parts they say battery, alternator and starter all tested and work fine. So we're not sure if it might have just been a bad connection, but at this point I'm going to drive as normal unless the car gives me a sign that is something else.
 

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Discussion Starter · #7 ·
Update...seems to be a reoccurring issue. Car has gone dead at least 4 times in the last several months. The first time was in April, I had the battery charged at advance auto parts and drove the car to the local Honda dealer...they couldn't find anything wrong during their diagnosis process. Then it happened again, this time I didn't get the battery charged but instead had a free towing to the dealer, this time they said the positive harness cable seemed to be worn out at the battery terminal... something they didn't notice the previous time. I paid about $900 for that harness to be relaxed. About 3 weeks later same problem again, car wouldn't start so I had the vehicle towed to the dealer again but they found nothing wrong in the charging system. It's now happened for a fourth time. Car has been sitting for 3 weeks as I had a recent ankle injury and have been recovering. My dad tested the battery voltage which was 2volts. Not sure what is causing this especially since both the Honda dealer and advance auto parts both indicate that battery, starter and alternator test fine. Any ideas? I really don't get how the dealership can't figure out the root of the problem so it's been frustrating. The last thing the dealership recommended was to put a battery tender on the car if I'm not driving it a lot but it's not like I'm storing the car for months... this is my daily driver and I wouldn't have any problems starting it up. It's been a reoccurring issue that started in ~Feb of this year.
 
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