Crash Data Retrieval System


Crash Data Retrieval System Nearly every new General Motors vehicle is equipped with a "black box," as shown in the photo below. The black box is more correctly known as the air bag Sensing and Diagnostic Module (SDM). The air bag module is the vehicle's "computer" that controls air bag deployment. Boster, Kobayashi & Associates has recently acquired a Vetronix Crash Data Retrieval (CDR) system to download and process pre-crash and crash data from a vehicle's SDM.
		The SDM consists of an accelerometer, lowpass filter, and microcomputer, which includes a data recording feature. While these devices are not quite as sophisticated as the flight data recorders used on airplanes, they capture and store data that can be particularly useful in reconstructing accidents. The current version of the SDM, in use on certain 1999 GM vehicles and nearly all 2000 model year vehicles (including passenger cars, SUV's and light trucks) captures and stores five seconds of pre-crash data including vehicle speed, engine RPM, throttle position and brake switch on/off status. Depending upon the particular vehicle, additional data may be captured.
Recordable air bag modules have been installed in selected GM vehicles since 1990. In 1994, GM introduced an enhanced module consisting of a single solid state analog accelerometer and a computer algorithm integrated in an SDM. The SDM computed and stored the change in longitudinal vehicle velocity (delta V) during the impact to provide an estimate of crash severity. It also added the capability to record the status of the driver's seat belt switch (buckled or unbuckled) for deployment and near-deployment events. There are two different types of SDM recorded crash events. The first is called the near-deployment event. A near-deployment event is an event severe enough to wake up the air bag sensing algorithm, but not severe enough to deploy the air bags. It contains pre-crash and crash data. The SDM can store only one near deployment event, and such event will be over-written by any subsequent event having a greater recorded velocity change, or it will be cleared from memory after the ignition has been cycled 250 times. The second type of recorded crash event is the deployment event. It also contains pre-crash and crash data. A deployment event is an event severe enough to deploy the air bags. This causes the SDM to permanently store pre-crash and crash data. Deployment events cannot be overwritten or cleared from the SDM and, therefore, can be retrieved at any time after an accident. Data can be retrieved from the SDM in one of two ways. If the electrical system of the vehicle is intact, then the data can be read by connecting to the vehicle's Data Link Connector. Located underneath the dash, it is used by technicians to talk to the vehicles on-board computer. If the electrical system is not intact, then the SDM can be accessed by connecting directly to the SDM's connector. A list of vehicles currently supported by the CDR is shown in Table 1. A software update to add GM vehicles for the 2001 model year is due to be released in the immediate future. In addition, an update to add vehicles back to and including the 1996 model year is planned for the near future. Eventually cables and software updates will be released that will expand coverage to GM vehicles dating back to 1990. Current CDR Vehicle Coverage (Click image to see full sized chart.) Other vehicle manufacturers also have recordable air bag modules, and the National Transportation Safety Board and the National Highway Traffic Safety Administration have recommended that all vehicle manufacturers equip their vehicles with recorders capable of storing crash data. For additional information, contact Michael Kreutzelman at (925) 447-6495.