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Discussion Starter · #21 ·
This question is related (and yes, I did use the search function first, but there are SO many posts about DO NOT DISCONNECT THE BATTERY).
On other forums I've been on, the manufacturer of the vehicle will have their people monitoring the posts and responding to help new owners.
I doubt any GM or Chevrolet employees monitor this forum, but if so, great.
Maybe somebody in this forum knows the answer.

I have owned maybe 60 cars in my life.
Worked on a lot more than that...maybe in the hundreds....
I have done most of the repairs on them all.
I've owned mostly Pontiac, a Buick or two, a few Oldsmobiles, many Chevys, one Ford, a few Dodges (and here comes the main question)
WHY is this vintage of Trailblazer so finicky with disconnecting the battery?
Of ALL the cars I've owned and worked on, I can't recall any where a person had to have the HVAC system recallibrated because one disconnects the battery.
GM...WHY did you design the vehicle this way?
 

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2004 chevy trailblazer_lt
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It is not just this vintage of TrailBlazer. Most every vehicle built in the last 20 years qualify for this precaution. Why? Because of all the computer modules that have been incorporated into the vehicles in order to minimize emissions, increase gas mileage, make things more convenient for owners, enhanced vehicular reliability (admit it, you love not having to change points every 12,000 - 18,000 miles), etc. Because of all these computers and minicomputer modules, every now and then something gets out of whack and their controller (or computer of minicomputer module) needs to be reset in order to go back to their original factory programming.

Going back to original factory programming is fine for electronic devices, but when you start having actuators that use nylon or other plastics for gears, and those items are over several years old (and likely out of warranty), running their recalibration routines, those brittle gears begin to break, and most people really like their AC in the summertime, and when that cooled air does not come out of the appropriate HVAC ducts, or their power door locks make noise but do not lock/unlock their doors, people go nuts, and when they find out it might take several hundred dollars in labor costs to replace a single HVAC actuator that retails for say $75.00, they go out of their minds.

Now, suppose you take your vehicle in to a responsible auto shop to have the battery replaced because it is on it's last legs. How would you feel if the shop did not use a KAM device to protect all those creature comforts and after they replaced your battery, you paid the bill only to find out that now your AC does not work right and the shop says "...we did not touch the AC system so that is a new problem and we are not responsible for it..."? So, using a KAM device makes good shop sense.

To coin a phrase from a commercial I heard years ago "...these aren't your father's Oldsmobiles..." This has never been truer.

As far as manufacturers having people monitoring various forums, maybe GM does have people monitoring this and the GMTNation forums, but from what I have seen on the GM-Trucks forum, the manufacturers representatives really only pay attention to those vehicles that are under the original factory warranty.

By the way, I am sure there are other vehicle manufacturers that also use gear driven HVAC actuators rather than the old wire cable connecting wire between the dash controller and the various doors in an HVAC system.

Does this help you any?
 

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Discussion Starter · #23 ·
Help? Kinda sort of, not really. I understand the usage of a KAM and why it is needed. I started mechanic school many years ago but stopped after 6-9 months because I realized with my back problems I would not be able to work underneath a hood because of the daily pain (I have a herniated disc b/t L4/L5).

I understand all of what you typed, but out of ALL the cars I have worked on in my life, this ONE Trailblazer that I own is the only one that I have seen/observed where when I disconnect the battery, I have to go to my local shop to have them recalibrate it. I do not have a Tech 2. I forget which scan tool I have...it is Ancel, but I forget the model. I cannot recalibrate the HVAC with the one I have.

My question was actually more directed towards a GM employee, because, like I said, this is the only one I have dealt with that has this problem.
 

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2004 chevy trailblazer_lt
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I would suggest you find a local GM dealer and ask to speak with the lead (head) technician in the service department. That individual will likely be the most experienced in the department, undergone the most GM training, and will likely be able to explain to you the reasons and rationale you seek.

I just accept that it is the way it is because of a whole lot of reasons.

Good Luck!
 
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I would suggest you find a local GM dealer and ask to speak with the lead (head) technician in the service department. That individual will likely be the most experienced in the department, undergone the most GM training, and will likely be able to explain to you the reasons and rationale you seek.

I just accept that it is the way it is because of a whole lot of reasons.

Good Luck!
Capitulation is the answer.

It's the way it is because it is. I'm sure that the same actuators in my '05 TB are identical (at least internally) to the ones used in and about the same vintage across the whole GM lineup ... maybe even Ford and Mopar.

Amazing as it might be to the OP --- gear sets of rack-and-pinion have been in use for decades in door locks --- where, against all anecdotal evidence --- they are not solenoids but a real spinning motor with a spur gear on the end operating a rack gear, which slides to move the door lock via a bent stiff wire --- or directly.

Auto part Circuit component Composite material Electronics accessory Cable


The motor is the big, silver thing-y.
 

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I've disconnected the battery numerous times. Didn't notice anything at all. Hell I didn't even know it was a thing until I started reading on this forum. Are you guys sure this isn't some kinda of voodoo cuz I cant wrap my brain around why this would be an issue, or why people think it is. What is it people think is happening?
 

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MrGrumpy, Welcome to the Forum.

Yes, we are sure this is not some kind of voodoo. It is a real thing. Welcome to the world of computer controlled vehicles and computer operated systems. All you need to realize is that the computers/various modules control virtually everything.

Want to start the vehicle, well when the ignition key is turned to the start position, the ECM looks at the input from the various information sensors before you can even realize it and then it commands the ground circuit side of the starter relay to close, commands the ignition system to power up, and multiple other commands are sent out, and then the vehicle starts.

Want to turn the headlights on - well when you turn the headlamp switch to "headlamps on", you are actually requesting the BCM (body control module) to allow the ground sides of the headlamps relays to complete thereby allowing current to flow to the headlamps to illuminate.

Now, when the vehicle is relatively young (and likely under warranty), the plastic gears inside the HVAC actuators are not brittle and the chance of them breaking during a power restored calibration routine is quite small. However, as time goes on, the chance of a plastic gear breaking during this process increases dramatically.

This help you to understand this any better?
 

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I work in the vehicle development/prototype field. Have been doing so the last 20 years, and currently still employed doing so. I've diagnosed, repaired and built idk how many vehicles the past 20 years. I'm fully aware of how computer controlled vehicles work, and I still fail to understand what the battery had to do with any of this. Keep alive memory only serves to store settings, configurations and emissions monitor status.

HVAC blend doors breaking is wear and tear, or possibly an assembly error when built, if it failed early and under warranty. Not because you disconnected the battery. They self calibrate themselves, OR some vehicles have a separate calibration procedure that must be followed using OEM diagnostic tools such as a tech2 or Ford VCM. They default to not working, or parking in one spot if not calibrated properly. Again, battery power has absolutely nothing to do with this.

As far as the BCM commanding on lights and other things, a majority of that could likely be traced back to a faulty BCM or wiring. But hey, I'm not gonna pretend that I know everything because I know I don't. I haven't owned this vehicle long enough to know. Im open to learning something new, I just don't understand the logic behind all this don't disconnect your battery hoopla. Disconnecting the battery should do nothing aside from reset your emissions tests, maybe your radio and HVAC temp settings and auto windows etc. If disconnecting you battery causes some kind of weird issue, the problem was pre-existing, and was going to fail regardless of the battery being connected or not.

Don't get the wrong here, I'm not saying these truck don't or won't have issues. I'm also not here to argue or pick fights or anything like that. It's just I've been working around many different types of vehicles my whole life and I just can't wrap my brain around this. Disconnecting the battery should never be an issue with any vehicle. The manufacturer does not design or build them this way. If they did, they'd have warranty claims through the roof.
 

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Keep alive memory only serves to store settings, configurations and emissions monitor status.
These blend doors use rotations of the gears to count the position of the door, when they battery is unplugged it forgets the location of the door, and must relearn it. The way that these motors learn is by opening and closing to their maximum spec, with the motors overvolting as the teach step. This teach procedure puts a lot of stress on the plastic components and they often break
 

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I agree with that, and I understand they must relearn their position. If it breaks however, this is a worn part and not the fault of the battery, or cause by disconnecting it. Its caused by old worn parts. So the issue is likely pre-existing worn parts, bound to fail at some point regardless IMO. It's the same with any car though. Not just envoys and trailblazers. Using a power source the keep the KAM alive, I can see preventing some of this, if you're afraid of fixing things that need attention, but issues don't fix themselves, and whatever potential issue you have with your vehicle is still going to be there. If you have an issue after disconnecting your battery, the problem was likely already there, or about to be.
 

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I agree with that, and I understand they must relearn their position. If it breaks however, this is a worn part and not the fault of the battery, or cause by disconnecting it. Its caused by old worn parts. So the issue is likely pre-existing worn parts, bound to fail at some point regardless IMO. It's the same with any car though. Not just envoys and trailblazers. Using a power source the keep the KAM alive, I can see preventing some of this, if you're afraid of fixing things that need attention, but issues don't fix themselves, and whatever potential issue you have with your vehicle is still going to be there. If you have an issue after disconnecting your battery, the problem was likely already there, or about to be.
There's a difference here that I think you might be missing. When the battery is connected and the HVAC actuators have done their initial relearn, their positions are set. The maximum and minimum movements are set in the computer and the actuators will not go beyond those positions no matter what hot/cold or mode setting you use. When the battery is disconnected, the slate on that data is erased. The computer must relearn what those min/max positions are. This pushes the actuators to their farthest rate of travel. You can only bend plastic so many times before it's structural integrity becomes compromised and they eventually break. Not disconnecting your battery will not cause the recalibration sequence, which will not stress the 20 or so year old plastic beyond it's capacity, which in turn prevents breakage. This is all caused by disconnecting the battery and causing the actuators to have to relearn everything again. Using a memory saver is great for remembering presets, and in this case saves us from having to essentially remove the entire dash assemble to replace some actuators.
 

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There's a difference here that I think you might be missing. When the battery is connected and the HVAC actuators have done their initial relearn, their positions are set. The maximum and minimum movements are set in the computer and the actuators will not go beyond those positions no matter what hot/cold or mode setting you use. When the battery is disconnected, the slate on that data is erased. The computer must relearn what those min/max positions are. This pushes the actuators to their farthest rate of travel. You can only bend plastic so many times before it's structural integrity becomes compromised and they eventually break. Not disconnecting your battery will not cause the recalibration sequence, which will not stress the 20 or so year old plastic beyond it's capacity, which in turn prevents breakage. This is all caused by disconnecting the battery and causing the actuators to have to relearn everything again. Using a memory saver is great for remembering presets, and in this case saves us from having to essentially remove the entire dash assemble to replace some actuators.
Thank you for explaining this better than I could have. I "understand" what he means by unplugging the battery doesnt break the actuators, but its because the battery gets disconnected that the car runs the sequence. It feels like semantics 🤷‍♂️
 

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Mike --- here's your problem with MrGrumpy ...

I work in the vehicle development/prototype field. Have been doing so the last 20 years, and currently still employed doing so. I've diagnosed, repaired and built idk how many vehicles the past 20 years. I'm fully aware of how computer controlled vehicles work, and I still fail to understand what the battery had to do with any of this. Keep alive memory only serves to store settings, configurations and emissions monitor status.
... he's locked into self-grandeur and cannot see outside of his self-aggrandizing box.

He obviously is NOT really aware of how computer controlled vehicles work or he'd say: "Hey --- I never knew that, but I'll certainly investigate it" ... and THAT would be the way a true scientific method would work.

Anecdotal proofs are tangible only to someone with an open mind. Field tests and clinical observations are certainly a foot into such reasons to investigate things that are out of one's personal comfort zone.

Some people learn from books on how to take a test and become certified ---- while others have field experience via "The School Of Hard Knocks" --- where most mechanics live and get dirty and actually repair things that cubical engineers design with zero hands-on.

We have dirt under our fingernails, so by extension ... we don't know what we're talking about.
 

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Thank you for explaining this better than I could have. I "understand" what he means by unplugging the battery doesnt break the actuators, but its because the battery gets disconnected that the car runs the sequence. It feels like semantics 🤷‍♂️
You get it, Brad. Thanks.
 

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Mike --- here's your problem with MrGrumpy ...



... he's locked into self-grandeur and cannot see outside of his self-aggrandizing box.

He obviously is NOT really aware of how computer controlled vehicles work or he'd say: "Hey --- I never knew that, but I'll certainly investigate it" ... and THAT would be the way a true scientific method would work.

Anecdotal proofs are tangible only to someone with an open mind. Field tests and clinical observations are certainly a foot into such reasons to investigate things that are out of one's personal comfort zone.

Some people learn from books on how to take a test and become certified ---- while others have field experience via "The School Of Hard Knocks" --- where most mechanics live and get dirty and actually repair things that cubical engineers design with zero hands-on.

We have dirt under our fingernails, so by extension ... we don't know what we're talking about.
Wow really? You think I'm arrogant huh. No I most certainly do know how computer controlled cars work. Just because you drive a PoS vehicle that breaks because you DONT know how to work on it, doesn't mean every time you disconnect the battery something is going to break, and that you should spew bullshit across the internet about never ever disconnect your battery or else. Parts get old, and break. That's a fact. Get over yourself.
 

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Wow really? You think I'm arrogant huh. No I most certainly do know how computer controlled cars work. Just because you drive a PoS vehicle that breaks because you DONT know how to work on it, doesn't mean every time you disconnect the battery something is going to break, and that you should spew bullshit across the internet about never ever disconnect your battery or else. Parts get old, and break. That's a fact. Get over yourself.
May you yourself, grow to a ripe old age ..... not.
 
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