All modern heavy truck engines have an Electronic Control Module, or ECM, the primary function of which is to control the engine’s performance, fuel efficiency, and emissions; to safeguard the engine from abuse; to troubleshoot mechanical problems; and to monitor the operation of the vehicle. In the event of an accident, the ECM may also record data that are useful in determining what happened. Exponent’s engineers have experience using ECM data in their truck accident analyses.
Depending on the engine make, model, and year, a truck’s ECM may record data surrounding a hard-braking event by the vehicle. Each engine manufacturer refers to these events by a different name, such as Hard Brake, Quick Stop, Sudden Deceleration, and Incident. Additionally, some ECMs can record Last Stop data. The type of data recorded varies by manufacturer, but typical data associated with these events include:
- Vehicle speed
- Brake application
- Percent throttle
- Engine RPM
- Cruise on/off
In addition to hard-brake data, a heavy-truck ECM may also record vehicle operational data around an engine fault code that might be set during an accident. The type of data depends on the manufacturer, but they are generally similar to those recorded during a hard-brake incident. The duration of the data recorded can range from a single data point to nearly a minute.
Other data stored within an ECM can be useful for purposes of accident analysis. For example, the engine configuration data, though not specifically related to the accident, can provide useful information regarding the vehicle at the time of the accident. Such data may include the vehicle’s maximum speed, engine horsepower, and programmed transmission and axle ratios.
Extracting and imaging of the ECM data from heavy trucks requires equipment and software specific to the manufacturer of the engine. Each make of ECM has specific characteristics that may induce a loss of data. These characteristics must be considered during the extraction process, and the post-accident condition of the vehicle can strongly influence the manner in which engineers retrieve the data. Exponent engineers are knowledgeable in the comprehensive and safe imaging of data from heavy-truck ECMs.
ECM data can be quite valuable in the analysis and reconstruction of a heavy-truck accident. However, the physical evidence is also important, and relying exclusively on the ECM data can lead to incorrect or unreliable conclusions.
When analyzing the ECM data, the accident reconstructionist must answer some crucial questions:
- Were the data actually recorded before/during the accident?
- Are the data reliable?
- Do the data appear to represent what we know of how the accident happened?
To answer these questions, the ECM data must be reviewed by a skilled heavy-truck accident reconstructionist in conjunction with the physical evidence. Engineers on Exponent’s heavy-truck team have the technical skill and knowledge required to integrate ECM data into a comprehensive and reliable heavy-truck accident analysis.