It has been recognized that Event Data Recorder (EDR) technology incorporated into the Electronic Control Modules (ECMs) of on-highway heavy truck engines can be a benefit to motor vehicle collision investigation and reconstruction [1,2,3,4,5,6,7]. Such beneficial features include the snapshots recorded by many Caterpillar engines. These snapshots, which are triggered by engine faults, operator input, or by what is called a “Quick Stop,” record engine operation and parameters surrounding the event. Past research has reported that while snapshot data are accurate, the documented event time may be off by 24 hours in some ECMs, notwithstanding the module's clock settings being correct . Furthermore, other research has suggested that some modules may report the time interval between data points at approximately two times the actual duration . In these cases, without a formal detailed study of snapshot records, the validity of the data may be brought into question should a snapshot be shown to have occurred on a different date, or should the timing of data be off.This study performed a detailed examination of the data recorded by Caterpillar snapshots. In particular, the research identified known issues, as well as several previously unknown anomalies that can occur with different Caterpillar ECM types. Beyond documenting snapshot data, the authors also explored whether or not multiple snapshot records can be recorded at the same time, or, when this is not possible, how much time is needed between events for multiple electronic files to be written.