2008 Trailblazer dimming / flickering lights

SpeedUp

Original poster
Member
Apr 15, 2017
115
McKinney, TX
My 2008 LS 4x4 4.2l has really bad dimming / flickering lights. This is headlights and interior lights.

Battery is fairly new, alternator is new. I checked the battery terminals, and they are tight. I looked at a couple ground spots and those are tight.

One thing I noticed is that when the car is off the lights seem normal, no flickering.

Any idea what this might be? Any common culprits?

thanks!
 

Sparky

Member
Dec 4, 2011
12,927
Is the reason for a new battery and alternator because of the dimming? Or did the dimming occur after replacing the alternator?
 

Boricua SS

Member
Nov 20, 2011
3,080
Ohio
Flicker? Like constantly or just every once in a while when the dimming occurs?

Dimming lights/slight flickering are common with this pigs. Most do the "big 3" upgrade to try and help with the issues which include the windows rolling up slowly as well, but i didnt notice a difference when i added extra cables. Now that i am cammed, my lights really dim and flicker with the lope of the cam, but it doesnt bother me.
 

SpeedUp

Original poster
Member
Apr 15, 2017
115
McKinney, TX
Not specifically - I purchased the car used. It was making a bad knocking noise, and other videos i watched suggested replacing the alternator. I did that, and it did not correct the noise. Next things on my list to replace are fan clutch, and water pump.

The battery is the one that was in the car, I have a receipt from previous owner showing its about a year old.

I am not 100% sure if the dimming was there before alternator swap, I was more focused on the knocking noise. I have only had the car a week.

The alternator is a duralast, I might get a delco one and swap it again to see if that helps.

The knocking noise that started all this goes away when the serpentine is off.

Flicker? Like constantly or just every once in a while when the dimming occurs?

Dimming lights/slight flickering are common with this pigs. Most do the "big 3" upgrade to try and help with the issues which include the windows rolling up slowly as well, but i didnt notice a difference when i added extra cables. Now that i am cammed, my lights really dim and flicker with the lope of the cam, but it doesnt bother me.

Yes, a constant flicker. When its flicking, I can see the battery needle moving up and down. It typically hovers around 14
 
Last edited:

budwich

Member
Jun 16, 2013
2,027
kanata
disconnect the SAVRC (the module on the negative cable... disconnect the connector). This should cause the alternator to run at 13.8v all the time as the system leaves the voltage control alone. It may help you identify whether its the alternator or something else there after.
 

Sparky

Member
Dec 4, 2011
12,927
Does the knocking sound and the pulsing match each other? Does the engine RPM vary with the knock and/or match the flicker/pulse of the lights? If you bring engine RPM up some, does it smooth out the flicker/pulse?

Take the belt off, spin each pulley by hand to see if you can identify that way what is making the racket.
 
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SpeedUp

Original poster
Member
Apr 15, 2017
115
McKinney, TX
The knocking and pulsing seem independent of each other. RPMs do not seem to affect the flickering.

I removed the belt and the noise went away, I hand spun the pulleys but they are smooth feeling and I cannot hear any noises.

Now I have a new issue, the battery light is going on and staying on.

Is this sounding more like a bad autozone alternator out of the box? I want to try a acdelco alternator but that will put me a couple hundred more in the hole. Of course if that is the fix no problem, but expensive test.

with the car off I am getting 12.4 volts on the battery
with car running, I am getting between 13.9 and 14.4 or so, this is while the battery light is on.

Those numbers are normal right ?
 

Sparky

Member
Dec 4, 2011
12,927
Those are correct numbers, but if it is an unsteady output that can throw the light.

When you say it is between 13.9 and 14.4, is it bouncing between there on your meter? If it is fluctuating that explains the flickering lights. Disconnect the module Budwich suggested and see if it stops the flicker or not. It very well could be a bad regulator in the alternator.

How loud is the knock sound? I think the fan clutch when going bad could be making noise... wait, you have a 2008, which should have a thermo clutch, not electronically controlled clutch... Hm.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
You could have the alternator tested and if bought recently, get it replaced on warranty.

For the knock, remove the belt and check each pulley and accessory, paying close attention to the water pump. It is a common failure item.
 
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