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I have a 2005 accord and have recently had the alternator and the battery replaced from the honda dealer. I then install the voltage meter on the cigarette lighter port. I notice the voltage output is at around 14V (good) while the engine is running. However, the voltage meter will occasionally show 12.6V. Sometimes, it will stay at 12.6V for a while, and sometimes it will show ~14V. Unfortunately, it's so random and I can't find a way to deterministically repeat it so I can show to the repair show. Is that the problem with the alternator or what? Any suggestion how to get that fixed?

  • Voltmeter in the cig port will not be accurate or reliable on the alternator output. Only accurate method is to connect it directly to the battery. – Moab Sep 30 '19 at 20:24
  • Are you actually having a problem with it starting or running accessories? – Pᴀᴜʟsᴛᴇʀ2 Sep 30 '19 at 21:01
  • After the alternator was replaced, there was one time stall when the car was idle for 10 min. I brought it back to honda and they are saying there's no issues with the starting system. Since I try to avoid the alternator issue, I bought the voltage meter that I can put on the cigarette port to monitor the voltage. I understand the cigarette port is not accurate, but if it's intermittently showing 12.6V when the car is running, it looks like to me something is not working correctly. – imhec3c Sep 30 '19 at 21:42
  • What is your climate? – mongo Oct 1 '19 at 17:40
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I suggest that you rule out an intermittent alternator. The symptoms could be quite similar, and would most likely be caused by failing brushes, which intermittently make contact with the slip rings. Another common failure mode is that a overrunning clutch on the alternator intermittently grabs and then releases, which results in a period of intermittent output.

I do not know if your engine has an alternator with an overrunning clutch.

If a wire is loose on the alternator connection it could cause similar issues. I understand that the alternator and battery were replaced, so perhaps your best best is to verify all the wiring.

A clamp-on current meter on the alternator output will tell you the alternator current output. The same clamp-on on the battery will give you an idea of whether the battery is charging or discharging, as you seem to be concerned about.

Knowing current flow is actually better information than knowing battery voltage, but since the lighter circuit probably doesn't have large loads on it, it will provide reasonably accurate voltage measurements.

So in summary, the likely issues are: intermittent alternator (clutch or brushes) and wiring or connector issues. The best diagnostic tool will be a clamp-on DC current meter.

  • Very nice answer! – DavidSupportsMonica Oct 1 '19 at 17:12
  • Thanks for the detailed explanation. I'll take a look at the wiring first for any apparent sign of improper connection or bad wiring. Unfortunately, this happens so random and I don't have a way to replicate the issue when I want. I did record the video that shows how the voltage reading toggling between 12.6V and ~14V. I hope this can be sufficient to prove the issue to the repair shop. – imhec3c Oct 1 '19 at 17:25
  • Well, you could have a large intermittent load, which pulls down your alternator, and drains the battery momentarily. Something like all your seat heaters coming on at the same moment. Just like in medicine, intermittent car problems can challenge the observational abilities of the operators, their systems knowledge and their creativity. – mongo Oct 1 '19 at 17:39
  • I've been keeping the loading to minimum when I tested the voltage fluctuation, even with the A/C and headlight turned off. So, I think that should rule out the large intermittent load. This morning when I drove the car for about half an hour, I didn't see the issue. On the other hand, in a short 10min drive yesterday afternoon, I did seen the issues and I recorded that in my phone. Can't find the condition to replicate that. – imhec3c Oct 1 '19 at 18:14
  • Good that you can capture on the phone, and hopefully your shop will pursue. Some will do better than others. It helps to have a good shop. Good luck, and tell us what you find. – mongo Oct 1 '19 at 19:36

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