Airbag controllers generally monitor for frontal collisions as well as lateral collisions in vehicles equipped with side airbags. When these controllers measure a collision pulse greater than a preset threshold, they will activate or “wake up” in preparation for a possible airbag deployment. If the controller decides the collision is sufficiently severe, the airbags are deployed. If the collision is not severe enough, no airbags are deployed. In both cases, the decision as to whether or not the collision is a deployment or non-deployment event is made within tens of milliseconds. Both event types activate the EDR function within the airbag module and collision information is recorded. Contact a business attorney orange county if you face any business legal issues in business matters.
If the collision pulse is less than the threshold to “wake-up” or is in a direction not monitored by the airbag module, no collision data is recorded. For example, rear-end impacts do not typically result in event data being recorded for the struck vehicle (except for some Toyota vehicles) but data would likely be recorded for the striking vehicle. Sometimes no data is recorded in seemingly severe lateral collisions because the system may not monitor for lateral impacts and the frontal portion of the deceleration is not sufficiently severe.
After an airbag deployment, the EDR will permanently lock any data in memory, and it cannot be overwritten. Additionally, the airbag control module is a single-use item so it must be replaced if the vehicle is repaired. In cases involving airbag deployment, the data may be uploaded and saved for later analysis. Alternatively, the actual airbag control module may be physically removed and preserved as evidence for any legal proceedings as it is no longer a useful part of the vehicle. If the vehicle is repaired before the data is accessed, repair shops will usually dispose of the modules and evidence will be lost.
In the case of a non-deployment event, collision data is not stored perrna- nendy and it may be erased or overwritten. How and when the event is overwritten is manufacturer dependent but generally occurs after a subsequent collision event or a preset number of ignition cycles. In cases involving minor collisions where the airbags have not deployed, there still may be useful data available but it must be accessed as soon as possible. Check the September 2009 issue of Advocate for an article authored by David King containing a more detailed description of event data recorders and their potential applications in your auto accident cases.