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2005 chevy trailblazer_ls
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251 Posts
Discussion Starter #1 (Edited)
This has been as problem for a little while now that tonight got much worse. I used to think it was just my eyes playing tricks. I'd get a flicker and then it was gone. Tonight it was just going crazy!

While costing or decelerating from a highway speed my dash lights and dome lights flicker madly as well as the volt guage bounces from about 12-16 volts.

It seems fine on acceleration, at very slow speeds or at idle. I brought it home, tightened the battery cables, they weren't really loose, I checked and cleaned the fender ground and looked at the power distribution cables. All visually checked ok.

I retest drove and still same problem. So while coasting I put the truck in neutral and shut the ignition off and then restarted the truck. All seemed fine???? The last thing I want to do is be stranded because I've ignored the situation!

I'm suspecting the ignition switch. I've read tons of posts on them and the problems they cause. Any other insight would be appreciated.

Battery load tested fine, Alternator load tested fine. It just seems to be something directly related to the vibrations from the road when the charging system is not capable of overcoming the issue.
 

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2005 chevy trailblazer_ls
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371 Posts
I have a similar issue, but mine only happens when the vehicle is cold. When I leave work I get on the interstate and do about 75mph for about 2 miles, then exit. As I am going down the ramp and the engine is at around 2000rpm, the headlights dim and the voltage gauge goes below 14v. It comes back up right away and never happens again during my trip home. It didn't do it all summer, but now that the temps are in the 50's when I get off of work, it has started again.

I think for both of our situations, it may be the voltage regulator. We just had a bus at work the other night that was doing what you described in your post. Any 12v accessory was seeing a pulse or surge of power. It was most noticeable in the headlights. We run a 24v/12v system and the 24v side was steady. The electricians replaced the equalizer and that didn't work so they tried the regulator and that was it.

Mine hasn't gotten any worse or better, but it is annoying. I wonder if there is a known issue with the regulators and the 05 Trailvoys?
 

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2003 chevy trailblazer_ls
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559 Posts
I had the same situation on my 89 300zx, i was drivng to jersey and all of a sudden my lights flickered and guages were going crazy, then it would stop if i passed 100mph once i let go of 5th gear it would do it again. Turns out it was the alternator. Just get a voltage meter and see if its outputting the 12volts.
 

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2005 chevy trailblazer_lt
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363 Posts
I have a similar issue, but mine only happens when the vehicle is cold. When I leave work I get on the interstate and do about 75mph for about 2 miles, then exit. As I am going down the ramp and the engine is at around 2000rpm, the headlights dim and the voltage gauge goes below 14v. It comes back up right away and never happens again during my trip home. It didn't do it all summer, but now that the temps are in the 50's when I get off of work, it has started again.

Mine hasn't gotten any worse or better, but it is annoying. I wonder if there is a known issue with the regulators and the 05 Trailvoys?
Sounds like your Secondary AIR system running its diagnostics.
 

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2004 gmc
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26,181 Posts
1) Bowhunt_Pro's problem, with the jumping voltmeter, smells indeed like the ignition switch or the ground that goes to the fender from the battery.

2) Audiojunky's observation sounds exactly like the dimming that comes from the diagnostic running for the secondary air injection pump. It turns on the 30 A turbine for a series of tests, a few minutes after start-up. People seem to notice it a lot more when the headlights are on, so leaving work in the dark after daylight savings time goes away in the fall, is usually the time I see more posts about the syndrome. Happens every year like clockwork.

The definitive experiment is to start the truck, and let it run 60 seconds before driving off, and that allows the diagnostic to finish before you roll. If you start up and drive off in the first 10-15 seconds, it interrupts the pump and the PCM schedules the test to be run later, after the engine warms up and under specific driving conditions. If this fails, it sets the famous P0410 code that's the subject of many, many threads.
 

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2005 chevy trailblazer_ls
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You guys nailed my issue! Great job! When I was having problems with my AIR system, that is when I would see the CEL come on. Don't know why I never put two and two together.

Bowhunt_Pro...is yours still acting up and have you dug in to the ignition switch yet?
 

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2004 gmc envoy_sle
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Same problem on 04 Envoy

I just had this symptom occur on my 04 Envoy. I have two questions: First, what is the AIR system/ air injection pump? Second, is this something I need to have serviced or can I just leave it be? Thanks!
 

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2004 gmc envoy_slt
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520 Posts
I just had this symptom occur on my 04 Envoy. I have two questions: First, what is the AIR system/ air injection pump? Second, is this something I need to have serviced or can I just leave it be? Thanks!
I've had the same thing happen to me. A "Search" will definitely enlighten :ugh: you to this common CEL problem. Mine goes away and comes back, repeatedly. I just make sure no other codes are present. Not going to the dealer after researching this on Trailvoy!
 

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2004 chevy trailblazer_ls
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207 Posts
Bowhunt I had the same problem as you discribed and I just checked the battery terminals. Then I got a pcmforless grounding kit then said :xit and drove from nc to ca with no other problems regarding the lights. Best I could tell is its just a hickup?

But just so you know when I get a chance im going to order a new ignition in the next couple weeks. Just for peice of mind and I read somwhere that its only like $30 and everyone says it WILL fail.
 

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I was having the same problem. Just started as the weather started getting colder. Did a search here and after some light reading decided to follow Roadies suggestion.......I have been letting in run for at least a min. in the morning before driving off and it worked. No more flickering head lights or dash lights. Ahhh, the power of "search"
 
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