99 Blazer LS Question

Newbie here. Just bought this vehicle a week ago. 4 door, 55K miles on it, paid $8900. While driving in the dark, I see a quick flicker in the lights, both instrument and headlights. I only drive a half hour to work and I see this flicker just once during the trip. I don’t know if I’d see it again if I drove longer. It occurs about 15 minutes after startup. The flicker is literally just a flicker, not something that hampers vision. Anyone know what might be the cause?

Thanks,
Deadeye

Nope, no idea, just keep an eye on the voltage guage, it should always be around the 14v mark or just a little above.

I have the same problem with my 99 Blazer. At first I thought it was my eyes playing tricks but it has happened enough that I know it's the lights. Every once in awhile, they will just barely flicker. No idea why, but just wanted to let you know you're not alone

Just for my information, does it happen with the defrost on?

Someone told me that the computer will cycle the AC compressor on every once in a while to keep the compressor from seizing up during the winter.

Wonder if that could be causing the flicker.

Mine happens without my defrost on, but the AC has been on. I'll have to watch that.

Sometimes the AC compressor kicking on will cause the lights to flicker slightly.

Mine occurs without the defroster on. No fan on at all.

yip, because the defrost usuaes you AC system to dehumidify the air.

i had a problem like that with my 95 jimmy. my headlight switch was bad. got damn hot with the lights on and just started flickering. 20bucks later i had niped it in the butt.

i hope you guys have an easy fix.

I have a 99 blazer LS and watched for the flicker and noticed it as I was pulling out of my driveway. Just a brief second and it was the defrost/AC compressor coming on as I turned the heater controller to defrost and floor.

Not a big deal, but was wondering and didn't put the compressor in my thoughts until I read this....

Thanks...another mystery cleared up.....

Best to only use defrost when you need it.

Using defrost will kill your fuel economy.

You sure it isn't the ABS system? When the vehicle reaches 3mph for the first time of each new engine start cycle, the ABS computer briefly energies the ABS pump motor as a self-test check.

This will cause a slight draw on the voltage system when the pump kicks on for a second or so.

About using the defrost, you may want to continue to use it, or atleast use it frequently. You want to keep the A/C system's seals lubricated.

Yes, as I said, using it only when needed will still run the AC system.

You don't have to run it constantly to keep the AC system running.

Some people keep it there all the time not knowing the drag it puts on the engine and the fuel economy it wastes.

Mr goodwrench said there's some kind of tech report on this but no recall. What we're seeing is a split second draw on the alternator. For $100 or so they'll replace the wiring harness to make the problem go away.

Since you never stated, does it occur when you first get the vehicle moving? As I mentioned before, at 3 MPH for the very first time the vehicle is moved upon that engine start, the ABS system will briefly kick on the ABS pump motor as a self-test at 3MPH. This is explained in the shop manual.

I have a '98 LS. At night time when I drive off for the first time after engine start, as soon as the vehicle gets moving, the headlights and interior dash lamps all dim for a split second as this ABS pump motor self-test occurs.

This actually is also something my Ford does, but around 19MPH. It is a common part of the ABS self-test to ensure that the pump and the circuit are working and will work if the driver needs the ABS.

my truck doesnt do the 3mph thing and my abs work fine, in fact, i just went about 5 mph into my driveways snow pile, and i know they are working

Perhaps it doesn't affect your charging system to the same degree. But it does cycle the pump for a brief second at 3MPH. If it didn't, it would set a trouble code and the ABS light would be on.

Edit, by the way, your vehicle must be moving 8 MPH or greater or the ABS system doesn't work, according to the GM factory shop manual.

shit, my truck doesnt see 3mph, lol that brief split second on its way up

I should state that as far as I understand, this occurs once the speed hits 3MPH or greater. So while you're passing the 3MPH mark, it will occur.

The manual states that you may hear this noise in the engine bay when it occurs. But other than that, you will not know that this occurs because the pump can run and not affect normal vehicle operation while it runs this brief test.

My truck does this every first time I hit 3MPH or greater. At night, I'll see the lights flicker, in additon to almost a crush type sound.

ive heard it b4 while strip crusin, so yeah, i guess it does it, kind of nifty... so the one time my abs light came on, the test failed? correct? why? and why only once?

There are many things that could fail which would turn on the ABS light. So honestly, no one could tell you why your ABS light was on one day. The only way you could know is if you had the computer checked for trouble codes. There are different degrees for certain faults. If it only occurred one time, and that has been a long time ago, I don't know if the abs computer would still have a record at that point of the cause. Someone more knowledgeable of this particular system would have to speak about it.

its nothing that did or does worrie me, it happend once, back in augest, right when i got it, and thats it, all it took to fix it was off then on again, but hey thanks, i learnd something new today

I think I may be seeing the flicker shortly after start as turbocpe describes, but I wouldn't say it happens everytime, but maybe I'm just missing it. But it also occurs at other times whether anything else is running or not.