John C. Glennon, Chartered has the equipment to download crash information for automobile Event Data Recorders (EDR). We provide complete EDR data analysis service as part of a crash reconstruction. To contact someone about downloading or analysing EDR data click here.


What is this Black Box?
Airbag systems in passenger vehicles have a computer whose primary functions are to receive inputs from various sensors and to use these inputs to determine if an airbag deployment is needed. This computer is also responsible for running diagnostics on the airbag system, for setting fault codes if problems are detected, and for turning on a dashboard warning lamp if a fault occurs. This computer goes by different names depending on the vehicle manufacturer but is generally referred to as the airbag module.

Some airbag modules have an added feature that allows them to store sensor data received by the module during an airbag deployment or near-deployment. These airbag modules, equipped with a Event Data Recorder (EDR) function, are often referred to as a "Black Box." Although, the airbag module is not a " Black Box", in the true sense of the term, this descriptor helps simplify the explanation of this device. Airbag modules with this EDR function do not record large amounts of data over long periods of time. However, they do record data from up to six sensors for a period of up to five seconds before an impact.

What Vehicles Have This EDR Function?
GM vehicles as old as 1994 have an EDR function that stores retrievable data. The number of older GM models with this EDR function is low, but the model coverage has increased each year after 1994.

Ford vehicles also have an EDR function that stores retrievable data. Ford vehicles as old as 2001 can be downloaded. Currently only about six Ford models are covered.

Many large trucks have an EDR function that is based in their engine's computer or Engine Control Module (ECM). These ECM based EDR's are different, and John C. Glennon, Chartered has different equipment to extract this data. Click here to find out more about large truck EDR downloads.

What Data Can Be Retrieved From the EDR?
Different EDR's have different capabilities in what they store. Most passenger vehicle EDR's have the capability of recording the measured deceleration from the crash. Other systems can store up to 5 seconds of pre-crash data including vehicle speed, engine RPM's, percent throttle, brake light switch position, and seat belt switch position.

How are these Data Retrieved?
The standard tool for downloading data from an airbag module with an EDR function is Vetronix Corporation's Crash Data Retrieval System (CDR). This system acts as an interface allowing a PC to be connected to and read the airbag module. Event Data is downloaded in code, and the software for the CDR System then coverts this code into a graphical form that can easily be read.

The CDR system can be plugged into the vehicle's diagnostic link located under the driver's side dashboard. If the vehicle's battery and wiring harness have not been damaged the data can be extracted by simply plugging in and turning on the key. If the battery is discharged or damaged, an alternative 12-volt power source will be needed. A portable jumper-pack is usually used for this purpose. If power to and communication with the air bag module cannot be made due to damaged wiring, the CDR can be hooked directly to the module. Certain precautions must be taken when powering damaged vehicles to prevent fire. Also, if the module is removed, stored data can be destroyed by improper handling. Only a qualified person should remove the airbag module.

What Can these Data be Used For?
The airbag module's EDR function is primarily intended to aid in the analysis of airbag failures. Capturing this data allows an analyst to see exactly what the airbag module saw during a crash and also the data it used to base it's decision to deploy or not to deploy the airbag.

The EDR data can also be used in the reconstruction of the accident. A reconstruction generally includes the analysis of vehicle speeds, impact angles, time-distance relationship of vehicles, etc. The most valuable data for reconstruction purposes are the measured deceleration from the crash and the pre-crash speed data. We stress that this data cannot stand alone, and should only be used as a tool to analyze an accident, just as any other evidence would be used. Generally speaking, investigators have a tendency to take this data at face value, but caution is in order.

This EDR evidence can be very valuable and provide a lot of insight into what happened in a collision. However, it must be analyzed in conjunction with other evidence to ensure its reliability. A reconstructionist must properly analyze and have an understanding of what the vehicle dynamics were prior to the collision. Then he must determine whether the vehicle's pre-crash dynamics affected the recorded vehicle speed. He must also know that the vehicle speed data comes from a vehicle speed sensor (VSS) that effectively measures the rotation of the wheels and, therefore, wheel speed and vehicle speed are not always the same. For example, a vehicle that is rolling-over with its tires off the ground, or sliding sideways, or braking hard, would have a wheel speed that is different than its forward speed. These factors would have to be taken into consideration to correctly analyze the data.

To learn more about large truck EDR downloads, click here.

To determine if you have a vehicle that has an EDR or to find out about getting an EDR download, please call us at 913-383-3856.