Voltage droop

[johnptfisher]

I have a 2005 trailblazer LS. When I bought the vehicle a couple months ago, I was driving home and the lights dimmed and the voltage dropped. I had the battery checked and found it was bad. Now on occasion the voltage will drop down to about 12.5 just for a second then back up. It generally maintains about 13.5-13.8 volts. Could the altenator be going bad or is there another underlying problem I should be looking for? I haven't had the altenator checked yet, but that is to come. I just want to see if anyone has has similar problems.

 

[Sparky]

I would double check to be sure the battery connections are tight. Then get the alternator tested.

 

[johnptfisher]

I would double check to be sure the battery connections are tight. Then get the alternator tested.

I should add that I changed the battery. All of the connections are tight. I had heard something about bad grounds could cause this as well. I'm really hoping its not the alternator as these are not cheap.

 

[Mooseman]

Could be the alternator. Get it tested. Could be the reason the battery got borked or the other way around is also possible if the alternator was overworked trying to charge a battery that was bad.

 

[The_Roadie]

Depends on if this is the classic SAIS (air pump) diagnostic test. Many folks, when they start driving home in the dark from work in the early winter, notice a light-dimming episode maybe 1-3 miles from work on the say home. If you're observant, you might notice it happening in three, one-second dips spaced a couple of seconds apart. If this is what you notice, we know what it is and can suggest some experiments to prove it. Otherwise it may be a flaky alternator.

 

[johnptfisher]

Depends on if this is the classic SAIS (air pump) diagnostic test. Many folks, when they start driving home in the dark from work in the early winter, notice a light-dimming episode maybe 1-3 miles from work on the say home. If you're observant, you might notice it happening in three, one-second dips spaced a couple of seconds apart. If this is what you notice, we know what it is and can suggest some experiments to prove it. Otherwise it may be a flaky alternator.

I have not had it in the winter time, however the three one second dips sounds about right. I will have to try and really pay attention to it, but that's what it seems that it does.

 

[The_Roadie]

The diagnostic happens all year round. I only mentioned the winter because that's the first time many folks start driving home in the dark, and they notice the diagnostic current draw and voltage droop in the dimming headlights because most folks don't have the voltmeter in their regular instrument scan. Every year for the nine years I've been on the forums we get an increase in this sort of question after daylight savings time goes away.

 

[orangeg8]

i had this trouble, and P0410 came on. I am looking on how to remove the SAIS, is it hard?

 

[The_Roadie]

Depends on how much salt and rust damage there is. No substitute for just getting down and dirty with a flashlight.

The voltage drooping from the SAIS turbine pump going off is not an abnormal event, though. There are about five things that could cause a P0410 code. Mostly I wrote my longest articles about how the system works and how to troubleshoot it back on trailvoy. You might want to run a Google search back there before replacing the pump.

 

[Decado]

Depends on if this is the classic SAIS (air pump) diagnostic test. Many folks, when they start driving home in the dark from work in the early winter, notice a light-dimming episode maybe 1-3 miles from work on the say home. If you're observant, you might notice it happening in three, one-second dips spaced a couple of seconds apart. If this is what you notice, we know what it is and can suggest some experiments to prove it. Otherwise it may be a flaky alternator.

The voltage drooping from the SAIS turbine pump going off is not an abnormal event, though.

Sorry to necro-post an old thread but I found many threads about this issue which I just noticed for the first time last night. As predicted, it was the first time I noticed and shortly after DST ends. The voltage dip happens exactly as you explain, in 2-3 short one second dips and then is fine. Headlights dim while down and then all is well.

Since this vehicle is still new to me I want to make sure nothing is wrong, otherwise I want to go back to the place I bought it from to have them fix it if this is not a normal operating condition. It sounds like this is a normal occurrence and something I should not be concerned about though, correct? What steps can I take to verify that it is indeed the normal SAIS diagnostic test running and not something else in the electrical system that I should be concerned about?

 

[The_Roadie]

I guarantee the SAIS diagnostic test is the issue. You can prove it by pulling the main fuse front #56 and the relay drive fuse #54. In a few drive cycles you may get check engine code P0410, but it's OK to drive with that code on.

 

[Decado]

Thank you.

 

[cyberpunk]

Depends on if this is the classic SAIS (air pump) diagnostic test. Many folks, when they start driving home in the dark from work in the early winter, notice a light-dimming episode maybe 1-3 miles from work on the say home. If you're observant, you might notice it happening in three, one-second dips spaced a couple of seconds apart. If this is what you notice, we know what it is and can suggest some experiments to prove it. Otherwise it may be a flaky alternator.

not to highjack here but.
i did notice this and will be honest with you for about a week my 04 sounded like a 747 taking off first thing in the morning after it sat all night. is this what i am experiencing then? the p0410 is on but everything i hear or states that it is ok to drive on. exactly like you say above happens in three i do see a slight voltage drop with some dimming and alternator tests good out or in vehicle. gm states that i just needed to replace the air pump.

 

[Envoy_04]

not to highjack here but.
i did notice this and will be honest with you for about a week my 04 sounded like a 747 taking off first thing in the morning after it sat all night. is this what i am experiencing then? the p0410 is on but everything i hear or states that it is ok to drive on. exactly like you say above happens in three i do see a slight voltage drop with some dimming and alternator tests good out or in vehicle. gm states that i just needed to replace the air pump.

Do the test (below) that the roadie described and see what happens. If the Boeing sounds and the dimming go away, the air pump is the problem.

I guarantee the SAIS diagnostic test is the issue. You can prove it by pulling the main fuse front #56 and the relay drive fuse #54. In a few drive cycles you may get check engine code P0410, but it's OK to drive with that code on.

If you want to just remove the system if repair or replacement of the pump is going to be super expensive, read through this thread in its entirety:

http://gmtnation.com/f23/removing-secondary-air-injection-system-3502/

Everything you need to know about taking out the system is in there, part numbers for the factory GM blocking plate and gasket (post 13 for plate #) and a good picture on post 51 of what all comes off to remove the whole thing.