Electronic Crash Data in Heavy Trucks and Buses

Detroit diesel electronic control module

Accidents involving heavy vehicles can result in large injury and damage claims. The key to resolving these claims efficiently and fairly may be contained in one of the many on-board computer modules found in modern vehicles. The electronic engine control module, or ECM, is the most common source of electronic crash data in heavy trucks and buses. Data can include speed, engine RPM, throttle, brake and clutch use for up to a minute before a crash and 15 seconds after. This data can shed light on key questions like whether a truck was being driven at an appropriate speed and in an appropriate manner before a crash or whether the driver responded in a reasonable way to an emerging hazard.

graph with speed, throttle, brake, clutch                                     Sample download data.

It is best to download ECM data soon after a crash because driving a truck, or even powering it up can alter crash data. Retrieving the data in a way that will withstand the tests of litigation requires expertise. Often a complete download requires two pieces of software; one used by fleet managers and another for service technicians. Relying on either of these parties can result in an incomplete download. It is also important to document the accuracy of the ECM clock and note certain truck features so that crash data can be correctly interpreted.

If the truck is relatively undamaged, module downloads can be conducted by connecting a laptop to a plug in the vehicle cab. If the vehicle electronics are badly damaged, then the ECM must be transplanted into an identical truck or a physical connection must be made directly to the module. Both of these methods introduce risk of erasing or overwriting data and should be performed by an expert.

Once crash data has been downloaded it can be tempting to rely on it at face value. However, due to some significant limitations it should be interpreted along with the physical evidence traditionally relied on by forensic engineers like tire marks and vehicle damage. Speed values, for example, can be incorrect if certain calibration values programmed into the ECM do not match the actual truck features, or the truck’s drive wheels were sliding on the road. Both of these inaccuracies have the same root cause: the ECM calculates the speed of the truck based on information from a sensor that measures how fast the truck’s driveshaft is spinning. This calculation relies on programmed calibration factors and is only accurate if the drive wheels are not slipping on the road (due to heavy acceleration, braking or yaw).

At MEA Forensic we have the expertise to properly download and interpret electronic crash data from heavy trucks. This data can be a key piece of a crash investigation puzzle.

Detroit diesel electronic control module               Detroit Diesel Electronic Control Module

For information on crash data recorders in passenger vehicles please see our Event Data Recorders page.

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