VIII. Electronic Control Module

Commercial truck tractors have an Electronic Control Module (“ECM”) responsible for monitoring and controlling important engine and vehicle parameters. The ECM is sometimes referred to as the “black box” for the truck and records data concerning the vehicle’s operation including speed, braking, use of clutch and use of cruise control. The type and amount of data recorded by the ECM varies according to engine manufacturer. The data can be downloaded with the right type of software.

The ECM may record data generally over a daily or monthly activity period and also when the tractor-trailer rapidly decelerates at a rate that exceeds a pre-set threshold. The threshold usually is met during a “hard braking event” but can also occur during a collision if the impact slows the truck down significantly. As part of a hard braking event, the ECM may record vehicle speed, clutch and brake status and throttle position. Certain ECMs will also record a “last stop” event whenever the engine is turned off. The ECM “last stop” data will be overwritten if the vehicle is placed back into service, and “hard braking event” data will be overwritten if the vehicle is placed back into operation and another hard braking event occurs. Because of the possibility that the data will be lost, it is extremely important to download any available data from the ECM as soon as possible after an incident.

A. Daily and Periodic Engine Usage Data from the ECM

The ECM may record the vehicle’s speed on a daily basis.

The ECM may also record the vehicle’s speed over a given period of time such as on a quarterly basis.

B. Hard Braking Event

We have included below a DDEC printout from the ECM of a Detroit Diesel Engine concerning a hard braking event.

The ZERO time is the point at which the ECM “woke up” as a result of the hard braking event. The ZERO time could correspond to the point of impact if the event that woke up the ECM was the impact itself, or it will be the point at which the truck driver began braking hard enough to exceed the minimum deceleration threshold, which could be either before or after the initial impact. The ECM goes back for a minute and records the data leading up to the hard braking event and continues to record data for several seconds after the hard braking event. In this case, the ECM has recorded  a number of items, but most important for an accident reconstruction would be (1) the vehicle’s speed; (2) whether the brake was engaged and (3) whether the cruise control was on.

C. Last Stop Event

The data from a last stop event is similar to the record of a hard braking event but the ZERO time is the point at which the vehicle came to a stop.

D. Types of Engines

The type of engine will determine what data is kept in the ECM and can be downloaded. We have included below a list of the different types of engines and the likely information kept in the ECM of each engine.

1. Detroit Diesel: May have engine and systems configuration data, trip/event data recording, two hard brake events, one last stop event, engine usage history.
2. Mercedes-Benz: May have engine and systems configuration data, trip/event data recording, two hard brake events, one last stop event, engine usage history.
3. Cummins: May have engine and systems configuration data, trip/event data recording, three hard brake events.
4. Caterpillar: May have engine and systems configuration data, trip/event data recording, one hard brake event.
5. Mack: May have engine and systems configuration data, trip/event data recording, two hard brake events, engine usage history.
6. Volvo: May have engine and systems configuration data, trip/event data recording, two hard brake events, engine usage history.
7. International: May have engine and systems configuration data, trip/event data recording, two hard brake events, two last stop events.

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