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Discussion Starter #1
Sometimes when I drive my 2013 Civic Si sedan, the headlights will randomly dim then get brighter, vacillating between bright and dim. I believe it happens to both headlights simultaneously. I don't think it's related to hitting bumps in the road. It happens only when the car has been sitting out in the cold for a while. After I drive for a few minutes, everything is fine. I haven't noticed any other electrical problems or flickering on the dash - all the indicators are steady.

What could it be??
 

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I had the same issue with mine. I thought it was the dual charging system. When it goes down to 12volts the lights dim and then back to 14 they brighten up. I even replaced the headlights with led to stop the headlights from doing it. Never noticed it doing it while driving as I've never had anyone I know driving with me to tell me.

Since then I've got flashpro and had the economy charging mode turned off and a new battery installed. Battery kept testing good for a year then finnally died.
 

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Discussion Starter #5
I checked the voltage after starting the car this morning. At first it was 14.4, but then the headlights starting flickering and the meter was swinging between 11.9 and 15.

I wasn't aware of the dual charging system. I'll have to look into that. I also plan to get the battery tested this evening.
 

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It's ELD system fellas. Altenator stops charging battery if it's full and low demand for power. Hence voltage changes and slight dimming of lights. It's a good idea not to mess with any of it unless you actually have a problem.
If you search you'll find more info, recently someone replaced a altenator after monitoring voltage, and the alternator caused real problems.
 

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I checked the voltage after starting the car this morning. At first it was 14.4, but then the headlights starting flickering and the meter was swinging between 11.9 and 15.

I wasn't aware of the dual charging system. I'll have to look into that. I also plan to get the battery tested this evening.
11.9 is too low. Probably need a new battery. Make sure it is load AND capacitance tested.
 

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Discussion Starter #8
Thanks to Janz3n! for clueing me in on the "economy charging mode." I disabled it with a FlashPro, and now I get a consistent voltage and no more flickering! Advance Auto said the battery is ok, so hopefully everything will be fine now. We'll see....
 

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FWIW, I had this same issue but I don't have a flashpro (yet). Now bear with me here... I had a 2 year old walmart battery and an AutoZone alternator. I ordered an OEM battery, OEM alternator, OEM belt, and OEM battery sensor. Unfortunately I can't tell you which fixed the issue because I don't have time to test every single part individually, BUT the problem is gone now thank god. My guess is the battery was the cause but the shop recommended the alternator be replaced regardless.

Guess I'm going OEM for the important stuff from now on...
 
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