What could make the headlights "pulse" when braking?

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2011 Mazda CX-9 Touring
My wife loved her 2013 Mazda3. But then a deer sacrificed himself on the front of her nice red coupe back in AUG 17. We ended up getting her a silver 2013 to replace it. Same hatchback style. Really the only thing different was she decided to go from a stick to an automatic. And it has been a great car. Except it does have this one quirk that baffles me...

During day time driving, totally normal. No quirks at all. But at night you put on the headlights... everything is fine... then you start to apply the brakes... the headlights visibly "pulse" as long as you are braking. Like supplying the electricity to the brake lights plus everything else plus the headlights is overloading the system and causing them to cycle up and down? First time I drove it at night, I thought I was imagining it. Then a friend drove it at night and asked about it. And it's the sort of thing, once you really notice... you really notice it!

I tried to tell myself this was actually some kind of "feature" that Mazda added to alert drivers you were braking... but the other 2013 didn't do it and it really seems more like a bug.

If I take it to my dealer and ask them to check "something..." what should that "something" be?

Thanks!!

Gregg Greenwood
Vinita, OK
 
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2014 Mazda3 S GT auto, 2008 MX5 6-speed
I would have the battery checked, especially if it is the original OEM one.
But really, if you describe exactly what you are experiencing, they should know to check the battery and its connections.
 
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2011 Mazda CX-9 Touring
65 views and my first actual Reply! I was getting worried.

I guess the battery itself is the first place to start. Seems like it is electrical somehow. It has started right up every time, even on cold winter mornings. We got it with like 55k on it, the wife just yesterday said she is up to 92k. So it probably is an OEM battery. But it has done this since we got it AUG 17. Not a new issue.

OK, I'll actually eyeball the battery and cables this weekend. I was just hoping somebody (or a lot of somebodies) had this happen in their Mazda3 and it was a known issue... with a known fix!

Thanks.
 
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2014 Mazda3 S GT auto, 2008 MX5 6-speed
Many years ago, the pulsing of headlights often pointed to a bad voltage regulator. Nowadays, the regulator is built into the alternator, so that may be suspect in your case.
 
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2011 Mazda CX-9 Touring
OK, thanks. It will be at the dealer for a recall in a couple weeks so I'll ask them to at least run an electrical test... we'll see what they find.

We drove it to Tulsa last night. (I'm not in that car at night very much since it is the wife's car.) I swear her low beams are more yellow/less white than I think they should be. Her high beams seem nice and bright but I wouldn't be very happy driving at night with those low beams. And the pulsing was very noticeable. I was the passenger and I would know instantly every time she even touched the brakes. Got to get it fixed and maybe that will also send more "juice" to the low beams! Somehow...
 
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Mazda 3iT 2012
My '12 did this. I found out there is a service bulletin on the problem. Dealer reprogrammed the PCM and it fixed the problem.
Don't know if it applies to the '13s as well. Ask your service department.
 
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2011 Mazda CX-9 Touring
Dealer reprogrammed the PCM and it fixed the problem.
Took the car in yesterday and explained the problem to the dealer rep.

He was skeptical about the solution but he did it.

Fixed!

Thank you!

Gregg
 
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2014 Mazda3 S GT auto, 2008 MX5 6-speed
I would've never guessed - good to know, as my son has a 2012 Mazda3 hatch.
 
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