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headlights dimming

9K views 17 replies 13 participants last post by  McKinley 
#1 ·
So last night i was on my way home, i had been driving for about 15 minutes on surface street sthen hit the freeway, when i ws at my exit another 15 minutes away, the headlights started dimming whenever i would hit the breaks. the didnt go out the would just pulse, it was like they were being drained of power and then would get it back. the dash lights were also dimming and the voltmeter was dropping aswell. it never dropped below ~12 or so and i havent driven yet today. Anyone have any ideas they would be appreciated.
 
#5 ·
I have noticed my headlights dimming/flickering at night also. I usually notice this at highway speeds when I let off the gas, the lights seem to flicker/dim a lot.

I am under warranty but if it's a ground cable loose I can check that but where are the grounds on the Trailblazer?
 
#6 ·
Follow the negative Battery terminal lead to it's ground point. Check and clean both ends.

Look for the Engine block to frame ground then clean and re-tighten both ends. Also check the Alternator connections for tightness.

:m2: B.
 
#7 ·
To the owners with the dimming/pulsing lights while coasting at speed, did this happen for you while it is wet out? My 2005 LS has done this, but only in the rain. I've yet to find the culpret connection.:mad:

Joel
 
#8 ·
for me it didnt happen in rain and it has only happened a few times since. the different times have been as follows

1- highway speed let off gas to exit and as i came up the ramp th headlights and dash lights dimmed and the voltmeter dropped to just under 14

2- same thing but driving around city doing no more than 50


it seems like it only does it when the car is decelerating(sp) but there is no brake applied. i havent even checked any of the wires because it has been such an infrequent problem but i think i may check them tomorrow.

Whats the worst scenario that this could be?
 
#9 ·
..it only does it when the car is decelerating(sp) but there is no brake applied.
Yep, same EXACT thing here. The dash lights & headlights pulse big time, but the engine never so much as stumbled or varied in RPM's. I havent gotten it to replicate in a few weeks. I hate those problems!

Joel
 
#11 ·
Actually, it's Just the "Design"

I have had the same issue, and I reseached the tar out of it. Ran across a few commentators that said it is part of the design. It seems that the voltage regulator is not a clean analog system - but has jump points. At certain load/charge ratios, it drops some of the alternator's charge. However, it does it in "bundles" - rather than smoothly. Thus, when you tap the brakes, add a little load, it may dump a much larger amount of charge, resulting in dimming all the way around until it gets around to rebalancing itself.

You can chase this problem for quite some time - but ultimately find out it is in the "design".

I just learned to get used to it. 175K on the vehicle and it hasn't caused any problems. I have found however that an Optima Yellow Top Battery seemed to smooth it out....

- WPK
 
#16 ·
I have had the same issue, and I reseached the tar out of it. Ran across a few commentators that said it is part of the design. It seems that the voltage regulator is not a clean analog system - but has jump points. At certain load/charge ratios, it drops some of the alternator's charge. However, it does it in "bundles" - rather than smoothly. Thus, when you tap the brakes, add a little load, it may dump a much larger amount of charge, resulting in dimming all the way around until it gets around to rebalancing itself.

You can chase this problem for quite some time - but ultimately find out it is in the "design".

I just learned to get used to it. 175K on the vehicle and it hasn't caused any problems. I have found however that an Optima Yellow Top Battery seemed to smooth it out....

- WPK
This is what I assumed based on the times that my '04 dims the lights... Not a big concern to me, I've seen subwoofers make lights dim much worse. Nobody but me even notices it. I am still on the original battery, so it's voltage is probibly not what it was, that could be making it more noticable.

But to the people that are actually bothered by it, I assume it's worse for you and could be another problem. Is your battery old or weak?
 
#12 ·
The problem when it happens does not stop the whole time while driving unless I am applying gas, doesn't matter if I brake or not. I see it happens constantly not just at a brake tap or anything. If it just happened once in a blue moon during a brake tap that would be acceptable.

So I don't believe what I have witnessed is by design since it's a safety issue with the lights constantly flickering/dimming. This effects both the driver and any traffic in front, other side of the road.
 
#13 ·
the problem went away for me for a while there, i hadnt had any issues but it arose again tonight and was worse than ever but only for about 5 minutes. whenever i would let off the gas they would dim, no brakes just letting off the gas. im going to try and take it into the shop soon to have them look at it, i will let you know if they find anything else it could be.
 
#14 ·
This is exact symptoms of the old AIR pump problem. Your AIR check valve is beginning to stick shut and the controller is ramping up the pump to compensate. It draws ALOT of current at full speed. This action is most prevalent at decel when the AIR system is operating. When the check valve gets bad enough, you'll be able to hear the AIR pump run during the self test after start up. If you hear the pump running from under the driver's door, then there's your problem.
 
#17 ·
I have the same issue, but it seems that after about 10-15 minutes of driving it wont happen anymore. They will however dim every time when i let off the accelerator from a cruising speed within the 10-15 minute range, doesnt matter how fast i was going. I used to worry about it till I saw a brand new TB do it also.
 
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