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At startup and low idle, lights dim and get bright


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Hi all, I have 12k miles on my 16 3500 6.7. Lately, at startup the headlights, backup lights, all dim ...


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Old 01-09-2017, 03:06 PM   #1 (permalink)
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Default At startup and low idle, lights dim and get bright
Hi all,

I have 12k miles on my 16 3500 6.7. Lately, at startup the headlights, backup lights, all dim and then get bright, dim and get bright as if the power is surging. My A/C is off and fan is not running. After a few minutes, this goes away once I start moving down the road.

Can anyone take a guess? Thanks


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Old 01-09-2017, 03:27 PM   #2 (permalink)
 
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Weak batteries. I would bet you have a slow drain somewhere.

You got a multimeter? You can look online or YouTube how to find a parasitic battery drain. I know it sucks and is not fun to do especially on a new truck with warranty, but it sure beats getting stranded somewhere.

The dealer probably won't do it because of the way warranty is paid. Warranty generally only pays a tech to fix problems, not find them. If the tech looks at your truck for a few hours and does not find anything wrong, then warranty will not pay him. So they will be looking at you to pay his time. This is why most people get the "we looked at it and found nothing wrong" on jobs like these because the tech does not want to work on anything he will not get paid on, and I don't blame him.


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Old 01-09-2017, 03:30 PM   #3 (permalink)
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Check your battery but it could also be the grid heater is cycling due to the cold weather. Check your batt level gauge at initial start. You will see the voltage goese from 12 to 14 V up and down.
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Old 01-09-2017, 04:25 PM   #4 (permalink)
 
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Default At startup and low idle, lights dim and get bright
^^This. It's your grid heater cycling until the intake gets warm enough. I asked the same question a while back, even posted a video. Got no responses. After some searching on other sites that's what I found. If you set your EVIC to show voltage you'll see it go from 12v. to 14v. Once it gets warm enough it will stop.
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Old 01-09-2017, 10:38 PM   #5 (permalink)
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Originally Posted by Mega-Hemi View Post
^^This. It's your grid heater cycling until the intake gets warm enough. I asked the same question a while back, even posted a video. Got no responses. After some searching on other sites that's what I found. If you set your EVIC to show voltage you'll see it go from 12v. to 14v. Once it gets warm enough it will stop.
Thanks for the info!! Yes, weather has been in the teens and low 20s when I start it. (update: This morning the temp was 46F when I started the truck, grid heater was not robbing power)


For anyone finding this in the future, here is what I found that explains the grid heaters and their function and how they cycle. http://blog.genosgarage.com/wordpres...-weather-tips/
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Last edited by champ198; 01-10-2017 at 08:29 AM. Reason: More info
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Old 01-09-2017, 11:11 PM   #6 (permalink)
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Here is a video I took Saturday. The temp wasn't 52, dumbo ears were in the sun. It was about 24 degrees. I could see the lights dim and wanted to catch them cycle.

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Old 01-10-2017, 06:28 AM   #7 (permalink)
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Originally Posted by The Hulk View Post
Here is a video I took Saturday. The temp wasn't 52, dumbo ears were in the sun. It was about 24 degrees. I could see the lights dim and wanted to catch them cycle.

What I noticed in the video is your voltage is dropping to 11 volts from 14 and then returning to 14 volts. That looks like the grid heater is cycling. What I find strange is that you see that much voltage drop at 1,100 RPM when the alternator (180 amp) should be able to produce 150 amps, and 190 amps for the 220 amp alternator. Disclaimer, I do not have first-hand knowledge since I have yet to drive my 3500 in cold weather.


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Old 01-10-2017, 09:55 AM   #8 (permalink)
 
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Doh! Forgot about the grid heater cycling in cold weather dropping your volts making your lights dim.

Sorry OP, my grid heater doesn't hardly get used where I am at and I tend to forget it is even there.


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Old 01-10-2017, 10:28 AM   #9 (permalink)
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Originally Posted by BossHogg View Post
What I noticed in the video is your voltage is dropping to 11 volts from 14 and then returning to 14 volts. That looks like the grid heater is cycling. What I find strange is that you see that much voltage drop at 1,100 RPM when the alternator (180 amp) should be able to produce 150 amps, and 190 amps for the 220 amp alternator. Disclaimer, I do not have first-hand knowledge since I have yet to drive my 3500 in cold weather.
My truck has snow plow prep so it has 220 amp alternator......I just wanted to get a video at high idle. It doesn't get very cold here and I was suprised at the voltage drop on the grid cycles.


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