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How is ECM (Black Box) Data Used in a Truck Accident Case?

Most 18-wheelers built since the 1990's have Engine Control Modules (ECMs), "black boxes" of a sort that record electronic data from various parts of the trucks during both standard operations and, in many cases, the times before and during a crash. But how exactly can ECM data help with a truck accident lawsuit?

Answer: By capturing important data about a truck's operation before and during a crash, an Engine Control Module (ECM) can provide helpful objective information about its cause and circumstances.

The Best Way to Understand Big Truck ECM Data is to First Think About Cars

An internal combustion engine is basically a small explosion-powered machine. The more precisely one can control the explosions, the better the engine operates. The whole name of the game in explosion control is maintaining a precise ratio of air to fuel. For a typical gasoline-burning passenger car, the ideal air to fuel ratio is 14.7:1, meaning that you have 14.7 parts air and 1 part gasoline, by volume. If this ratio is not maintained, the engine doesn't run correctly.

Now, achieving this ratio of air to fuel is trickier than it sounds. Altitude, humidity, air temperature, contaminants in the air, and numerous other factors conspire to make the proportion between air and fuel to go off target. After all, one does not burn "air" mixed with fuel. Rather, one burns the oxygen in the air mixed with fuel. So, the wetter, hotter, thinner, or dirtier the air is, the harder it is to get the right amount of oxygen to mix with fuel and burn cleanly inside the engine.

To address all of these factors, a modern car engine is controlled by a small computer. Said computer is the ECM that we speak of. The ECM is connected via wires and cables to various sensors placed on and near the engine. These sensors measure air temperature, throttle position, air pressure, air flow, exhaust gas temperature, etc. The computer uses the data from these sensors to make small adjustments to the air to fuel ratio.

Specifically, the engine takes whatever air is in the environment the engine is operating in at the time. You can't change the air without going to some new location. What the ECM can change is the amount of fuel that is sprayed into the engine, which then mixes with the air and is ignited. The ECM starts out by assuming that there is a baseline "correct" amount of fuel to spray into the engine, and then it takes measurements and adjusts the amount of fuel that is sprayed into the engine based on the readings from the sensors. This all happens many times per second.

The takeaway here is that the ECM exists first and foremost to run the engine.

But when a computer is taking readings for the purpose of running the engine, it stores this data temporarily. When an accident happens, all that data stays in the computer's memory, and it can be extracted by someone with the right electronic equipment.

Of course, the purpose of that data was to make the engine run right, but certain facts about the accident can be gleaned from the data. For example, if the ECM data shows that the engine was at 3,500 RPMs with some particular engine load, an engineer could easily determine how fast the car was going, even though the ECM wasn't specifically trying to record the vehicle's speed. That said, many modern cars actually do specifically record things like vehicle speed or what gear the transmission is in, and some even specifically record accident data.

The reason we chose to focus on passenger car ECMs to introduce you to this idea is that an Otto Cycle gasoline engine is at least somewhat familiar to most drivers. And understanding what the ECM is trying to accomplish is therefore easier to explain.

For the Diesel engines in big trucks, however, a somewhat more complicated process occurs, but it's still functionally the same in that the ECM regulates the supply of fuel so as to control the ratio of air to fuel.

What Other Information Does the ECM Record?

Some ECMs are more advanced than others and record data such as:

  • "Hard" braking or sudden stops;
  • Power steering activity;
  • Whether cruise control was active;
  • Position history/GPS;
  • The truck's speed in the time just prior to impact;
  • How long the truck was in service before the crash; and
  • Engine load in the truck.

This is not a complete list of the information that an ECM may be able to provide, but the general idea is that it often contains many quantifiable details to help experienced accident reconstructionists better understand a crash. Different manufacturers install different types of ECM and the data they record may vary, but most provide helpful data to those trained to get and interpret it.

How Does ECM Data Help Crash Investigations?

Some information gleaned from ECM data may seem pretty straightforward; for instance, if it shows a tractor-trailer was speeding or hard-braked just before plowing into traffic that could be an indication that driver negligence (falling asleep, distracted driving, impairment) was a contributing factor. Other data points may not be as clear, but they can still tell important parts of the story. For example, seeing that a truck operated long beyond its permitted hours of service could be a sign that its driver was exhausted or perhaps unfairly (and illegally) overworked by their employer.

On its own an ECM isn't necessarily a "smoking gun" proving trucker misconduct, but the information it contains can often clarify or support investigators' findings during accident reconstruction. The more specifics they can learn, the better picture they can develop of not only what happened, but also how and why.

How Can ECM Data Help 18-Wheeler Accident Victims?

Truck condition, truck driver behavior, and many other crucial data points can be measured and reported by the truck's ECM. If the truck driver did something wrong or the truck malfunctioned somehow just before a wreck and victims' subsequent injury, the information in the module can be crucial in proving it—particularly as trucking companies are unlikely to simply admit fault without substantial evidence proving it. On that point, it's important to realize that the company owns that ECM and its data and is unlikely to hand either over unless it has to. If a truck's ECM data is overwritten or erased vital evidence might be lost.

That's where a good truck accident lawyer can make a huge difference. Attorneys with the right knowledge and experience will conduct thorough investigations of a truck accident, collect and preserve every source of evidence (including ECM data), and use their findings to build a clear and convincing case on their clients' behalf.

The Texas attorneys at Grossman Law Offices have decades of combined experience helping those injured in 18-wheeler crashes; if you were hurt or lost a loved one in a collision with a commercial vehicle, call any time for a free consultation.

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