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2012 Chevy Impala Ignition Cycle issue...

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2012 Chevy Impala Ignition Cycle issue...

Post by bryanrauf » Sat Nov 19, 2016 11:06 am

I am analyzing CDR information from a 2012 Chevy Impala involved in a T-bone collision. The Impala suffered front end damage and the driver airbag deployed. As a result of the collision I had to backpower the module to download the EDR information because of the collision, no power was running to the ignition.

The EDR data shows 1 deployment event, 1 event only on the dynamic counter, and all the speed, and passenger information seem to fit, etc. But the ignition cycle at investigation is 134 cycles higher than the ignition cycle at event. There was no power to the vehicle so the ignition could not be turned over to run. What could cause this? And if an airbag deploys but is not replaced or reset, would the ACM still record possible future deployment events?

Thanks for information you can provide, have a great one! :)

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Re: 2012 Chevy Impala Ignition Cycle issue...

Post by actar670 » Thu Dec 08, 2016 8:19 am

The ignition does not have to be "turned over to run" to record and ignition cycle. While you may have used a technique to backpower the ACM to do the download, you haven't mentioned why you had to backpower in the first place. Was the key in the vehicle, was the battery disconnected, were there electrical problems with the vehicle at the scene of the collision before the battery was cut that might have produced a bunch of voltage fluctuations, did someone else turn the vehicle on/off 133 times before you applied power to the ACM, etc.?

I had a crash a couple years ago that I worked on where one of the vehicles was involved in a prior collision, and then purchased by someone who attempted to rebuild the vehicle a bit at a time. He started with repair that were just sufficient for him to get the vehicle back on the road and inspected, which included replacing the driver and passenger airbags. He did not replace the ACM, even though the airbag light would not go off, as the vehicle was still driveable and it the light didn't really bother him all that much. When he was involved in this frontal crash the airbags he replaced actually deployed, however, the data I retrieved from the ACM didn't seem to make any sense when compared to the witness statements and the scene evidence. Since the ACM was not replaced after the first crash and the data on the ACM was locked because the airbags had deployed in the first crash, the data I retrieved was from the initial crash, not the one I was investigating.

Even though the speed and delta-v data was the first sign of a problem in my case, when I looked a the data more carefully I observed that the ignition cycles at download were nowhere close to the "at event" ignition cycles. In your case, you would have to have an airbag deployment that occurred relatively recently in the history of the vehicle in order to be similar to my case. I would start with a vehicle history report and see if the vehicle has been involved in any other crashes where the airbag deployed. If there is no history of a prior crash with an airbag deployment you are that much closer to relating the data to the crash you are investigating.
Bruce McNally
McNally & Associates ARS, LLC
41 Champlin Ridge Road
Rochester, NH 03867
Office (603) 516-4560
Web http://mcnallyassociates.com

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Re: 2012 Chevy Impala Ignition Cycle issue...

Post by bryanrauf » Mon Dec 12, 2016 7:38 pm

There were electrical issues... with the battery connected, the key was turned but nothing lit up, the car was "dead". But funny enough the green light was lit on the interface indicating power was flowing to the EDR and through the DLC. History of the car had no previous crashes... thanks for your input!

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Re: 2012 Chevy Impala Ignition Cycle issue...

Post by KentBoots » Tue Dec 13, 2016 9:58 am

Bryan,

Out of curiosity what did the battery voltage measure?

For clarification remember the green light being illuminated on the CDR Interface only means there is power at the CDR interface; nowhere else. Further the green light being illuminated does not indicate there is sufficient power to conduct Crash Data Retrieval.

Pin #16 on the DLC is always hot when there is a good battery and intact electrical system, but that doesn't mean the ACM is getting power.
Kent E. Boots
FactualDiagrams.com

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Re: 2012 Chevy Impala Ignition Cycle issue...

Post by bryanrauf » Sat Dec 31, 2016 12:16 pm

I didn't check the voltage of the battery at the time.


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