Tractor Trailer Accident Investigations and Electronic Control Modules

A collision with a semi tractor trailer can result in catastrophic injuries or death. Thorough investigation of a tractor trailer accident is critical to your case. One tool at our disposal is the technology found in many of today’s tractor trailers.


What is an Electronic Control Module (ECM)?

An Electronic Control Module (“ECM”) is a small computer that collects data in modern passenger vehicles.[1] All modern, heavy trucks (i.e., tractor trailers) are equipped with ECMs.[2] The basic function of ECMs is to control and monitor the vehicle’s operations.[3] This includes recording information such as engine performance, fuel efficiency, cruise control, climate control, mechanical problems, airbag systems, and speed-controlled stereo volume.[4] ECMs also run diagnostics, detect problems in the vehicle, and turn on dashboard warning indicator lamps.[5] If a vehicle is in an accident, certain ECMs record data that can help explain what happened.[6]

What is an Event Data Recorder (EDR)?

ECMs that are capable of recording crash data are equipped with an Event Data Recorder (“EDR”) function.[7] Usually, the recording function is triggered by an event that is associated with an accident such as hard braking.[8]  Engine manufacturers may refer to these triggering events by a variety of names including “Hard Brake,” “Quick Stop” or “Incident.”[9] Typically, EDRs do not record data over a long period of time;[10] however, some EDRs do store certain pre-crash data such as vehicle speed for five to twenty seconds prior to the crash.[11]

While this recording function varies between vehicles, many large trucks have some type of EDR function.[12] The type of data that is recorded varies by manufacturer, but typically includes vehicle speed, brake application, percent throttle, engine RPM, and whether cruise control was on or off.[13]

How Event Data Recorders Help Accident Investigations

The data recorded by ECMs can be very valuable when analyzing an accident. Data extraction requires professional engineers that are familiar with the process.[14] Each manufacturer requires specific equipment and software to extract the ECM data.[15] It is important to review all physical evidence of an accident, as well.  In order to provide reliable accident analysis, an accident reconstruction expert or ECM expert must analyze the reliability of any ECM data and consider the data in conjunction with any physical evidence.[16]

[1] ECMs, also referred to as “modules,” may go by different names depending on their manufacturer, or the system they control.  Some examples include: Powertrain Control Modules (PCMs), Body Control Modules (BCMs), Engine Control Modules (ECMs) or Airbag Control Modules (ACMs).


[3] Id.




[7] ECMs with Event Data Recorder (EDR) functions are sometimes generically referred to as a “Black Box” similar to those found on airplanes.  An ECM is not a true “Black Box,” but the description helps explain the function of the device.

[8] See

[9] Id.


[11] Id.

[12] Id.


[14] Id.

[15] Id.  Some manufacturers also provide specific training and certification.

[16] Id.