Consequences of Disconnecting Battery

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Here is a short list of some of the problems that can occur when disconnecting or replacing the battery on the following vehicle applications (refer to the OEM service literature for specific model and year applications and cautions):
  • Chevy Tahoe Loss of voltage to the vehicle electrical system causes the 4WD module to go to sleep permanently. The module never wakes back up when power is restored, and the only way to restore normal 4WD operation is to replace the module with a new one (a repair that may cost you over a hundred dollars!).
  • Mercedes (various models) Loss of voltage to the vehicle electrical system will prevent the A/C from working. The climate control module must be reset to restore normal operation. It may also disable the Stability Control System. The ABS module has to undergo a relearn procedure for the steering angle sensor to restore normal operation.
  • Toyota (various models) If the battery is disconnected while the key is on, it can set a fault code for the airbag system and turn on the airbag warning light (which deactivates the airbag system until the fault is cleared with a scan tool).
  • Subaru (various models) Disconnecting the battery can trigger the anti-theft system, preventing the vehicle from starting when the battery is reconnected.
  • Saturn L-Series The body control module may forget the odometer display reading. Nice if you are selling a car and want a 0 mileage reading, but expensive to fix because it requires replacing the BCM (at a cost of $300 to $400) and reprogramming the odometer reading.
  • Honda (various models) Disconnecting the battery will set a code and turn on the air bag light (which also disables the airbag system). The dealer must reset the system with a scan tool to restore normal operation.
  • BMW, Audi & VW (various models) Disconnecting the battery requires numerous module relearn procedures which can take up to several hours with a factory scan tool

What happens when the battery is disconnected? It depends on the year, make and model of your vehicle, but any of the following may happen:
  • Loss of learned values in the PCM's Keep Alive adaptive memory. This may cause the engine to run poorly because the air/fuel mixture is too rich or too lean for a period of time until the PCM can relearn the fuel trim adjustments. This may take up to several days and 50 to 100 miles of driving until engine operation returns to "normal."
  • Erasing the PCM's adaptive memory may also affect the way the transmission shifts and feels. The transmission may not feel the same until the PCM or transmission control module relearns the shift adjustments. This may take 50 to 75 miles of driving.
  • It resets the FMEM (Failure Mode Effects Management) module on certain late model Ford vehicles. This module provides an adaptive fail-safe strategy that substitutes estimated or fixed data for missing sensor data. Normally, this should not cause a problem UNLESS the vehicle has a bad sensor and has been substituting data from the FMEM module for a missing input.
  • It resets the ABS (Antilock Brake System) and SIR (Supplemental Inflation Restraint) or airbag modules. This should not be a problem UNLESS one of these modules requires a special relearn or reprogramming procedure after power has been lost. In that case, the affected module may prevent the ABS or airbag systems from working.
  • It resets the Climate Control module. On some vehicles, the module will not start working again until a special relearn procedure or reprogram procedure is performed with a factory scan tool. That means no A/C until the module is programmed with the correct instructions.
  • It resets the Body Control Module (BCM). Like the Climate Control module, the BCM may not resume normal operation until it has undergone a special relearn procedure or is reprogrammed with a factory scan tool. This can mess up the operation of power accessories such as power windows, memory seats, power sunroof, or electronic suspension settings. Worse yet, the BCM is the "gate keeper" module on many 2003 and newer vehicles that have a CAN (Controller Area Network) system. If the BCM cannot communicate properly with all of the other modules, or it does not recognize the addresses of other modules, it can cause all kinds of problems.
  • It may reset or disable the anti-theft system. The engine may crank but not start because the anti-theft system thinks somebody is trying to steal the vehicle. Again, it may require a special relearn procedure or reprogramming the anti-theft system with a factory scan tool to resolve the problem.
  • Loss of power window and/or power sunroof position settings. Unless power is maintained to the vehicle's electrical system during battery replacement, the power windows and/or sunroof may not work properly until the position values have been reset using the vehicle manufacturer's relearn procedure.
  • Loss of steering angle sensor settings. The steering angle sensor will have to undergo a relearn procedure following battery disconnect or replacement.
 
Joined
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The Chevy Tahoe seems more like money grab, I wonder how many people will have not bought this car if they knew about this little problem.

I like Volvo's but the newer cars are just too crazy w/ many modules which are not only expensive to buy and need a software down load.
Just crazy.
 
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On vehicles like the Tahoe it would be better to get more specific info because the 4WD module might be common to other GM’s. I don’t have any problems with disconnecting on my 4WD Burb. Having said that, who can recommend a good 12 volt bypass setup.
 
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On Toyota it clears the DTCs and also resets the DTC clock, odo, and warmup cycle count. If that is something that matters to you.
993FABA8-11FA-4444-8E68-4A73A07FBDC3.jpeg
 

SubLGT

Thread starter
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So, short of never disconnecting the battery......what are some commonly available solutions to prevent some of the above?
"Memory Saver" devices, such as:
The Schumacher OBD Memory Saver Cable is another handy device for preserving
learned data, stored codes and programmed electronic settings such as
clocks, radios, seat positions, keyless entry systems, alarms and more.
The cable supplies voltage to the PCM by plugging one end into a 12-volt power receptacle on another vehicle,
and the other end of the cable into the OBD connector on your vehicle.
Just make sure the 12-volt receptacle on the other vehicle is ON and is supplying voltage
before you disconnect your battery.
 
Joined
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That list is very broad... I never has issues with our MB and BMWs with battery disconnects. Usually the only things required where: setting date/time, synchronization of windows and roof and completing drive cycle.

Very broad is an understatement.
 

4WD

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Did not find anything in the owners manual on the Tahoe 4WD module claim … just stuff on BLM etc …
So, considering changing the battery on our 2017 because I never get over 4 years in the Texas heat …
Anyone use a Noco ”settings keeper” (plug in dash outlet) … ?
 
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Besides the Schumacher there is also a C-TEK model that has a setting to keep all the memory while changing the battery.
Oh shade tree mechanic where art thou? Gone to war with the tchies! :oops:
 
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Anyone use a Noco ”settings keeper” (plug in dash outlet) … ?
I used the Solar branded one, same thing. Back feeds through the OBD port. Gotta be careful not to ground the positive battery cable, or you'll blow whatever fuse feeds said port.
 

4WD

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I used the Solar branded one, same thing. Back feeds through the OBD port. Gotta be careful not to ground the positive battery cable, or you'll blow whatever fuse feeds said port.
Noted … Will stick short piece of pipe insulation over that terminal … Thanks
 
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What about using a fresh 9 volt battery connected across the two battery cables? if you take more than 5 minutes to change the battery this might not work, but most of us could do it fast enough.
 

4WD

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The Noco is 9V and was $20 … so I ordered one from eBay … we will see …
 
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modern vehicles can be a PITA with TOO MANY gadgets + NANNIES so i dont buy them, even DI is a no-no for me!!!
 
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The Noco is 9V and was $20 … so I ordered one from eBay … we will see …
For your new battery take a look at an auto store sourced AC Delco 42 month maintenance free. Not sure how maintenance free does in the Texas heat but my last one made it 7 years up here. Here’s a pic of the new one I just bought. Don’t mind the dust. I also like them because they line up perfectly with the large red belt that the positive cable has on GM’s. (Not sure if the 2017 has it). :)

C129086C-68CB-4196-B91F-0F9544A260B7.jpeg
 
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4WD

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For your new battery take a look at an auto store sourced AC Delco 42 month maintenance free. Not sure how maintenance free does in the Texas heat but my last one made it 7 years up here. Here’s a pic of the new one I just bought. :)

View attachment 39124
I can look around - but off hand don’t know of a parts house here that has ACD
🧐 got me thinking maybe the dealership can put one on the insurance tab since the airbags & other safety systems sucked the life out of the OEM battery … have always assumed they are never the same once drained out the first time
 
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I changed my battery this weekend ( first time in 7 years) on my 2008 Burb and low and behold I did not lose my radio station settings or my automatic seat position settings. ( and the 4WD worked fine) “I don’t know how’s youse did that but I know youse did that!” :p
 
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