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  1. #1
    MembersZone Subscriber rmoore's Avatar
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    Dec 1998
    Plano, Texas

    Default Don't Let the Cops Tell You Different...

    Here's a great Post to keep in your files next time the cops try to intimidate you into thinking you've done something wrong. The original question, from a metro NY City fire officer is presented first then the reply from my GM contact.

    "I have a question in regards to disconnecting the battery at MVA's. An Assistant Chief on my job has asked me to find the answer and I told him I would try my best.

    I know you stress (and rightfully so) the importance of disconnecting the battery ASAP at MVA's. Our Police Dept (ESU Division mainly) is complaining that by disconnecting the battery, we are killing the computer, thus they loose any information stored in it for their police investigations, if it has to be downloaded afterwards.

    I know the computer serves important in the function and operation of the vehicle, just as "the brain" of the SRS; but they are making it sound like it is the equivalent of an aircraft's "Black Box".

    Do you have any information or know where I can find it, in reference to this question and the suggested SOP's?"


    The cops claiming that the data unit would lose all its information because we killed the battery didn't make sense to me. What difference would it make anyway. We're going to kill the power so we don't have problems during the patient care and removal from the vehicle. That's first priority anyway. Well, it didn't take me long to get to a great source at GM. They've had 'black boxes' on selected GM models for years so I knew my contact would be up on this. It was no surprise. We are right and the cops are mis-informed. Kill the power; just like we've been doing.

    Here's the "word" from my insider at GM, and you can take this to the bank!

    "Hi Ron!
    You are right. The Sensing Diagnostic Module(black box) saves crash data from a deployment forever. It can be hooked to at any time and be read. Once the ignition source to the SDM is removed, any information, whether volatile or not will be saved until it is next powered up. This information will be saved at key off, or battery disconnect."
    Ron Moore, Forum Moderator

  2. #2
    MembersZone Subscriber
    Join Date
    Nov 2003


    They have a back up lithium battery in the ECU to be able to store info that lasts practically a life time.
    In a lot of crashes the 12 volt battery is destroyed from the impact,so to say that you would lose information by disconnecting it is false! if it needed that particular power source to save info to the ECU and there is enough damage to render the battery useless from impact then where would the info be if there was not a back up system.
    Vetronics is a brand of software that downloads blackbox info from most popular vehicles, Check out their website for info on this.
    The only way information can be lost is by a secondary impact in the same area of the vehicle where the crash occured,this is called a rewrite.. so now the secondary crash info is now stored in the ECU over writing the first.
    There was a situation where a tow truck driver was backing up to a vehicle involved in a crash and accidently hit the front bumper quite hard and over wrote the first intial impact's history contained in the ECU.

  3. #3
    Forum Member firenresq77's Avatar
    Join Date
    Oct 2000
    Northwest Ohio


    Thanks, Ron!!!

    See, maybe NYPD ESU should take a lesson and keep their nmose out of the rescue work!!

    (That is a joke for those who didn't notice it)
    The comments made by me are my opinions only. They DO NOT reflect the opinions of my employer(s). If you have an issue with something I may say, take it up with me, either by posting in the forums, emailing me through my profile, or PMing me through my profile.
    We are all adults so there is no need to act like a child........

  4. #4
    Forum Member Bones42's Avatar
    Join Date
    Mar 2001
    Pt. Beach, NJ


    Unfortunately, I know some Extrication Instructor's who give the same advice (not removing power).
    "This thread is being closed as it is off-topic and not related to the fire industry." - Isn't that what the Off Duty forum was for?

  5. #5
    MembersZone Subscriber
    Join Date
    Nov 2000
    Rendon, Tx, Tarrant County


    What vehicles can these black boxes be located in?

  6. #6
    Forum Member nmfire's Avatar
    Join Date
    Nov 2002
    Maryland (DC Suburb)


    Are you saying that if you turn the ignition back on, it erases everything? That doesn't sound right.
    Even the burger-flippers at McDonald's probably have some McWackers.

  7. #7
    Forum Member Rescue101's Avatar
    Join Date
    Jun 2001
    Bridgton,Me USA


    We've dealt with two near fatal crashes recently.In both cases we had SP come in and they were able to download the info at the time of impact.Of course they still "map" the scene like they always have but the ability to get that electronic snapshot is very helpful if and when the case goes to trial.Some pretty neat technology. T.C.

  8. #8
    MembersZone Subscriber rualfire's Avatar
    Join Date
    Jun 2003
    Strathmore, Alberta, Canada

    Default case study


    A case study. Validates the traditional accident investigation methods, and I'm sure is powerful data when the reconstructionists are sitting on the witness stand.

    Doesn't say much about the issues discussed here relating to removing power though.
    Last edited by rualfire; 05-27-2005 at 10:02 AM.

  9. #9
    Forum Member
    Join Date
    Feb 2003


    In our area a fire scene is just that, it is run by FD and FD only. If you want to find good doughnuts, then listen to a cop

  10. #10
    MembersZone Subscriber GDDYUP's Avatar
    Join Date
    Oct 2003


    Here's some info for ya concerning SDM...

    "How It Works

    The SDM is basically the airbag "brain" that has a small amount of memory. Within milliseconds of a collision, a vehicle's SDM senses the crash severity and determines whether to deploy the airbags. Crash severity is measured by the vehicle's loss of velocity over time, known as "delta-V." The airbag deployment signal is also a signal to store data in the module. Once an airbag is deployed, the deployment record is permanently written. The data cannot be erased, altered or cleared, even if the battery is disconnected, the SDM becomes unplugged due to the force of the collision, or from emergency workers and investigative personnel. Once the airbags are deployed, the SDM must be replaced if the vehicle is repaired.

    Newer GM airbag modules have has the added capability of recording crash data even when a vehicle's airbag doesn't deploy. The SDM is able to do this because there are two memory slots: one to record an airbag deployment event, and the other to temporarily record an airbag near-deployment event. A near-deployment event is when a vehicle sustains an impact that "wakes up" the airbag module, known as "algorithm enable," but the SDM determines the impact is not severe enough to deploy the airbags. Once written, a near-deployment record is cleared after 250 ignition cycles (equivalent to about 60 days of driving), or the record is overwritten by a new impact if it is greater than the previously stored near-deployment record."

    You can see more about how this all works via this link...

    Accident reconstruction and GM's "Black Box"
    IAFF Local 4392

    "From this day to the ending of the world,
    But we in it shall be remembered:
    We few, we happy few, we band of brothers;
    For he today that sheds his blood with me
    Shall be my brother..."
    Shakespeare's King Henry V

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