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The Electronic Control Modules (ECM) installed on heavy truck engines record data during normal operation. While their primary purpose is to control the mechanical and electrical systems on the engine, they monitor other vehicle systems as well. Stored data from the ECM can be downloaded into reports that are useful for tracking fleet performance, scheduling maintenance or troubleshooting engine problems. Many of the current production heavy trucks also record event information that may be useful when analyzing or reconstructing accidents. It is not uncommon for a vehicle involved in a frontal accident to experience sudden decelerations and/or sustain damage to the coolant system or rupture the oil pan. Sustained data outside normal operating parameters from sensors on the engine will typically trigger the ECM to generate a fault code. On a Caterpillar ECM, a short event record called a Diagnostic Snapshot may also be generated with a fault code.

Heavy duty truck and engine manufacturers have been installing various forms of electronic Event Data Recorders (EDRs) on their products over the past decade, the most common being the Electronic Control Module (ECM). The primary purpose of the ECM is to control electrical and mechanical systems on the engine. As well, it monitors other vehicle systems. The ECM stores data in a manner that allows reports to be generated that aid fleet managers to monitor the performance of their equipment and that assist mechanics to diagnose problems. Some of the data in these reports can be of value in accident investigation and analysis even though these reports may not have been originally intended for this purpose. This paper discusses the specifics of data collection from the various ECMs and the reliability of such data when used for the purposes of accident analysis based on testing.