dangers when disconnecting battery on Trailblazer

[greggraves]

Thought I'd start a new thread about this. As you may know, disconnecting the battery on a TB may or may not result in your computer reset process breaking one of the HVAC actuator doors. That will cost you. It cost me. I talked with the dealer and they always hook up a 'computer memory retention' tool to prevent this and other bad things happening when you have to disconnect the battery. Here is a Youtube about this: Trailblazer battery disconnect - side effects - YouTube

I don't have the tool, but I am thinking that this homemade tool would work fine.

neg.battery.clip ----------------- neg.post.9V.battery pos.post.9V.battery ------------- diode-> ------------------- pos.battery.clip

attach the pos.battery.clip to the positive post on the battery; connect the neg.battery.clip to a good ground. Remove the negative battery cable. Do whatever. Replace cable. Remove my patented (ha) memory sustainer.

The diode would keep the 12V current from flowing backwards through the 9V battery and potentially blowing it up/ruining it.

Good idea? Bad idea?

 

[The_Roadie]

Should work. The diode reduces the 9V battery voltage by 0.7V, but I'm pretty sure the various memories in the modules retain their data with as little as 8V.

The factory battery uses side terminals, and those are harder to clip to and less secure because the bolt floats in the insulated ring lug body, but you could certainly clip to a good ground and the threaded stud on the front fuse block where the red wire ring lug should go. Then you have no worry about erratic connections through battery cable bolts.

 

[meerschm]

Might be cleaner to get a 12 volt round adapter and put the batery inside the car, plugged into the accessory (used to call this a ciggie ilghter)

Amazon.com: Computer Memory Saver: Automotive

something like this.

 

[triz]

I've never had the issue, "knocking on wood", but going to add one of these to my toolbox. Plus it will keep me from setting up the stations all over again.

 

[MAY03LT]

Yeah just today someone posted about a misfire that popped up after a battery swap. Plus he probably had to set the clock which is no fun.

Before they made dedicated memory savers, and before we had crap like retained acc power or modules that would self-power down after X minutes, the 9v/cig savers were popular. I don't know if I'd use one today because there wouldn't be enough reserve if the dome lights turned on or something similar happened.

 

[The_Roadie]

... Plus he probably had to set the clock which is no fun....

Wussies. Yer all wussies.

 

[greggraves]

Good point: dome light comes on 9V cheezy battery voltage goes to zero, memory gets lost. So 9V idea is no go. Solution is to buy an 8 battery D cell holder. They are like 4 bucks plus shipping:

12BH181-GR Eagle Plastic Devices | Mouser

Mouser generally sells quality stuff, so the battery holder you are looking for is made by Eagle

radio shack sells a 4 battery holder for 3 bucks and it has a wire coming out of it to simplify construction.

 

[hockeyman]

The factory battery uses side terminals, and those are harder to clip to and less secure because the bolt floats in the insulated ring lug body, but you could certainly clip to a good ground and the threaded stud on the front fuse block where the red wire ring lug should go. Then you have no worry about erratic connections through battery cable bolts.

Would it be possible to hook up a battery jumper to both +/- fuse block terminals while replacing the battery? ...Or will that be too much stress on the fuse?

I even have a battery charger with a 6v & 12v setting, with Low and High recharge rates. Sorta looks like this.

 

[{tpc}]

I purchased one that plugs into the OBD II port for something like $11 at Autozone. On one side is OBD, the other side is cigarette lighter plug. Is designed to plug into a jump starter pack, some of which I guess have a cigarette lighter adapter on them. I didn't have this available so I used one of those gray radio shack plug in power supplys that are 13.8V that had a cigarette lighter plug on the front of it, and that worked just fine. I would be careful whatever you do and double check polarity.

There are more expensive solutions out there, but they aren't really worth it if you have a power source of some sort available. I too could have made the cable myself, but for the cost, it was just easier to buy it.

 

[MAY03LT]

Would it be possible to hook up a battery jumper to both +/- fuse block terminals while replacing the battery?

Yeah that would work. The positive lead could go to the "input" positive stud of the fuse block, and the ground could get grounded to the....well, I'm not sure where the optimum grounding spot would be. Maybe the factory ground at the L/F strut tower or the engine block.

 

[Machoman]

What gauge wire would you use?

 

[The_Roadie]

14-20 AWG. Whatever you have in stock.

 

[glfredrick]

I purchased one that plugs into the OBD II port for something like $11 at Autozone. On one side is OBD, the other side is cigarette lighter plug. Is designed to plug into a jump starter pack, some of which I guess have a cigarette lighter adapter on them. I didn't have this available so I used one of those gray radio shack plug in power supplys that are 13.8V that had a cigarette lighter plug on the front of it, and that worked just fine. I would be careful whatever you do and double check polarity.

There are more expensive solutions out there, but they aren't really worth it if you have a power source of some sort available. I too could have made the cable myself, but for the cost, it was just easier to buy it.

I've heard about the problem with battery disconnect but never experienced it myself on a vehicle, but this thread convinced me to just go out and get the cable. Ordered from Amazon and on the way. I'll use a jump box and a direct to OBDII cable from now on. I don't want to have to dig into the heater box if at all possible. Re-setting the other stuff is no big deal, but taking the whole dashboard apart sort of sucks.

I ended up getting this one because it has on-board diagnostics to make sure that one is actually saving the memory instead of blowing a fuse, etc. Seemed a good idea and just a tad more money than the cheaper varieties (i used the Amazon prime price and paid less).

Amazon.com: Schumacher (OBD-L) OBDII Memory Saver Detector: Automotive

 

[{tpc}]

I've heard about the problem with battery disconnect but never experienced it myself on a vehicle, but this thread convinced me to just go out and get the cable. Ordered from Amazon and on the way. I'll use a jump box and a direct to OBDII cable from now on. I don't want to have to dig into the heater box if at all possible. Re-setting the other stuff is no big deal, but taking the whole dashboard apart sort of sucks.

I ended up getting this one because it has on-board diagnostics to make sure that one is actually saving the memory instead of blowing a fuse, etc. Seemed a good idea and just a tad more money than the cheaper varieties (i used the Amazon prime price and paid less).

Amazon.com: Schumacher (OBD-L) OBDII Memory Saver Detector: Automotive

The one I used is a Schumacher as well, but just not as fancy as that one. If they would have had it at autozone, I would have bought it.

I agree about not digging into the dash. I'm kinda on the fence about bad hvac actuators should die. On one hand I agree, and I agree at some point they probably will die. On the other hand, I want to be able to make that call and messing with these while it was still cold on my wifes truck wasn't an option for me. In the summertime, maybe. I'm more worried that I wouldn't be able to complete fixing it over a weekend, and I have no backup car for the wife to drive (other than mine). My actuators probably would have been fine, but taking the chance during the winter wasn't worth it.

 

[chucki]

so could I use the boat battery and jumper wires and hook to a good ground and hook to where the "red" wire is supposed to hook and replace my battery without any issue?

 

[Sparky]

Just turn off the dome light (override switch) before disconnecting the main battery. No biggie.

Can't say I've ever had an actuator die because of disconnecting the battery. I had one wear out and start clicking from wear that I had to replace before it totally died (it still worked just sounded bad), but it wasn't from a battery disconnect.

The way I see it, if disconnecting the battery "kills" the actuator, it was gonna die anyway.

 

[KNBlazer]

The way I see it, if disconnecting the battery "kills" the actuator, it was gonna die anyway.

agreed....first time battery was disconnected actuator died, no front air.... I wonder if this is only a risk you run on certain years and only on original actuators...

 

[northcreek]

Don't even waste your time making a memory saver. I bought one at Wally World for $6 with the battery...Mike.

 

[The_Roadie]

agreed....first time battery was disconnected actuator died, no front air.... I wonder if this is only a risk you run on certain years and only on original actuators...

In my experience, it's a risk for any actuator that's weak. Impossible to tell ahead of time by year or age or mileage or model number. It's like a kid - if you could tell before they were born whether or not they'd be a lazy goof, you could plan around that. As it is, you can only run stress tests on them when they reach certain ages, and see how they react. And better to run the stress tests on YOUR schedule than wait until they go away to college or something, then you find out they can't handle taking a test without you hovering over them with the answers.