ECM Data is Critical in a Truck Accident Investigation

Michael GrossmanFebruary 21, 2025 6 minutes

It's not uncommon for those of us writing on this site to advocate for independent investigations after serious 18-wheeler accidents. Some see that as common-sense advice, but more than once we've been asked: "What will another investigation do that police don't already take care of?"

I understand the skepticism, but decades of work in this field have shown me that law enforcement officers, important and dedicated as they may be, may not have the time, training, or resources to dot every "i" and cross every "t." For example, I've seen far too many police investigations that ignored a crucial source of evidence in just about any commercial truck accident: The engine control module, or ECM.

Engine Control Modules and Truck Accident Investigation

For those who may not know, the ECM is an internal computer that basically serves as a "brain" which controls crucial engine functions like proper air-fuel mixture, emissions, and ignition timing. It also records data about how it was driven, noting variables like speed, braking, and seat belt usage.

If you think all that stored data seems like something police should want when determining how an accident happened, you're right; objective information free of any bias or subjectivity is an asset to any investigation. Since "black box" recorders are usually associated with airplanes, think of it that way: When a plane crashes, investigators often put together a theory about how that happened before they ever go near the black box. Does that mean they should just go with their gut and leave the data untouched? Of course not.

Just like the airplane's black box, a commercial truck's ECM record might strongly influence investigators' conclusions. Some may think I'm saying the computer will inevitably show a truck driver was careless or his vehicle was faulty, but its data could reinforce the trucker's version of events just as easily as it can disprove them. Despite all that, I have seen information suggesting ECM data is only obtained by police around half the time during 18-wheeler crash investigations. Why is that?

Why Don't Police Always Include ECM Data in Their Reports?

There are a few possible reasons why police don't always include ECM information in their investigation reports. Some of the ones we run into most often are listed below.

The ECM Was Destroyed

In terms of reasonable explanations, one of the most obvious is that the ECM simply didn't survive a major wreck. Considering the sheer size of an 18-wheeler (especially a loaded one, which can weigh up to 40 tons), it's very possible for its engine compartment to be destroyed during a crash. Since that's where the ECM is usually found, the collision may destroy it too. It also doesn't stand much of a chance if the truck bursts into flames, which is a known problem due to the saddle gas tanks on many commercial trucks.

That kind of destruction certainly happens, but nowhere near 50% of the time during truck accidents—which is also why someone needs to verify that the ECM was destroyed if a trucking company claims that occurred. If it wasn't destroyed, though, what other explanations might there be for not obtaining it?

Police Don't Know how to Access/Read the Data

People may not always consider this, but investigating any given traffic accident is only a small fraction of an individual officer's duties—and gets an even smaller fraction of a department's resources. Many officers get only limited training in traffic investigation, most of it geared toward drawing conclusions from witness statements and physical evidence at the scene. If they don't have the technical training to download and read ECM data, asking them to do either won't get you very far.

Police Work for the State, Not for You

Another thing that stands in the way of an effective 18-wheeler crash investigation is that police aren't specifically there to help the victims; their actual job is to find out if any crimes were committed by anyone involved. If evidence shows a truck driver was drunk, distracted, speeding, or did something else illegal, he may be charged, but criminal guilt isn't the same as civil liability. Police findings may sometimes help accident victims as evidence in a lawsuit, but their efforts aren't specifically geared toward helping build a civil case against the truck driver or his employer.

Officers Can't Just Seize ECM Data

As agents of the state, police are a little hamstrung in what they can collect for their investigation—and for good reason, as the Constitution's fourth amendment protects citizens from arbitrary search and seizure. An engine control module is the private property of whoever owns the truck it's in, meaning officers can't pull it out without permission or a warrant—and neither of those are necessarily easy to get. Trucking companies obviously aren't keen to hand over potentially-incriminating evidence, and judges typically don't issue warrants for police to examine private property unless officers compellingly show that the property could contain evidence of a crime. Since the majority of truck accidents don't involve criminal offenses, and any related cases are usually matters of civil law, it makes sense that police wouldn't bother getting a warrant to look at ECM data just to write a trucker a speeding ticket.

With so many factors stacked against them, it's a testament to the professionalism of police officers that truck accident reports get as much right as they do. However, when the issue is what caused a serious or fatal commercial truck accident, "close to the truth" isn't the same thing as knowing exactly what happened. That's why truck accident attorneys often take action to find the details police didn't get to.

How Do Attorneys Get Evidence the Police Don't?

While both deal in legal matters, that's more or less where the similarities between police and attorneys end. Lawyers stay busy, but unlike police officers their attention isn't constantly demanded by a hundred other job responsibilities. They are far more able to focus on the needs of their clients, especially in terms of holding the people who hurt them accountable. That means they have the time and the resources to get evidence that police leave behind—including the ECM and its data. But what exactly do attorneys do differently?

Spoliation and Subpoena

The first tool an attorney has that a police officer lacks is a letter of spoliation, which puts a trucking company on notice that they're being investigated. Receiving such a letter means the company has a duty to preserve any evidence relevant to the investigation, including the truck's engine control module. If the trucking company destroys or "misplaces" evidence after receiving a letter of spoliation, then the court may penalize the company further down the line in ways that make it harder for the company to defend itself.

Another valuable weapon in an attorney's arsenal is a subpoena, which is a court order that compels a trucking company to hand over evidence. A subpoena can sometimes be far more effective than a police warrant, because even though a trucking company has plenty of defenses in a civil proceeding, its protections are more robust in criminal cases.

Believe it or not, truck accident injury attorneys have those powerful investigative tools at their disposal as soon as they file a case. Couple that with their ability to devote more time and attention to a client's accident, and you see why attorneys can often round up evidence police can't or don't.

ECM Data Should Never Be Left Out

To be clear, ECM data isn't some magic bullet that makes all other evidence unnecessary. Useful as it is for providing context and data during a case, it's not foolproof and probably wouldn't make or break a lawsuit on its own. It's just that any responsible investigator will gather as much evidence as possible, from every available source, and use it to learn the whole story. If half of all truck accidents never involve ECM data analysis, that's a lot of unfinished stories.

That's not to suggest police do a bad job. For the reasons we mentioned above, sometimes they're not in a position to go over an accident scene with a fine-toothed comb the way they should. They do a fine job with most accident investigations, and I don't want to say otherwise. I'm just saying that a second, closer look is often needed when serious injuries result from a crash—particularly a commercial one, because a careless truck driver and the company that put him on the road are very unlikely to cooperate or make amends of their own free will.

I realize that many people probably don't care much about ECM data or what goes into a good investigation. Hopefully they'll never be in a position where they have to care, but if they do they'll want the best investigation they can get. One way to determine whether or not they're getting that is to check whether the police report includes any mention of engine control module data. If it does, things may be on the right track; if not, another look may be needed.