Understanding Your ECM

Jul 24, 2018 | Articles

Understanding Your ECM

By Bruce C. Mallinson

It’s been 19 years since the first computer-controlled electronic diesel engine for semi trucks has been released. These days, just about everything on the engine is monitored and controlled by the engine computer, also commonly referred to as the ECU (Electronic Control Unit) or ECM (Electronic Control Module). And each year, these electronics become more and more integrated in the truck. Just being good with a wrench doesn’t cut it anymore. Today’s technicians need to truly understand the electronics and the ECM.

Think of your truck’s ECM and its electrical system being similar in function to your body’s electrochemical nervous system. The ECM is the brain and can “feel” problems through its wires and nerve-like sensors. If sensors are the ECM’s nerves, then solenoids (including injector solenoids) can be thought of as the “muscles” that the ECM controls.

Sensors are designed to produce a specific range of either electrical resistance or voltage that changes with temperature, pressure or in the presence of an electromagnetic field. Each sensor typically makes a single signal circuit that feeds into a pin on the ECM. The ECM powers the sensor through a sensor supply and sometimes a sensor return circuit, and then monitors the sensor signal wire by watching the voltage range the sensor sends back. If the voltage drops too low or goes too high, the ECM will let you know by turning on a warning light. The ECM will tell you where to look by giving you a code that identifies a specific circuit and condition. Your brain does this as well, and will quickly let you know if you’re touching something that’s outside of your comfort range – like a hot exhaust stack.

Compared to your nervous system, an ECM is very dumb. Most ECMs have no way to verify what the truck is actually doing. The ECM is simply reading a voltage and making an assumption. Because of this, ECMs are easily fooled.

I once had an ECM tell me it was reading a turbo compressor outlet temperature of 1,600 degrees – while at idle! Remember, the ECM is just a machine. It didn’t actually know that the temperature was actually 1,600 degrees – it was only going by what voltage it received from what it thinks was its temperature sensor. When ECMs do crazy things, like read 1,600 degrees at idle, don’t assume the ECM is bad. There is a big difference between an ECM that is bad and an ECM that is simply being fooled. The ECM that is being fooled is doing its job correctly. What is not working correctly, in this case, is the electrical circuit or sensor the ECM is monitoring.

Among technicians in the trucking industry, the most widely misunderstood part of the truck is the ECM. As a result, the ECM has become a scapegoat for almost any problem the technician fails to identify. A mechanical problem that a technician fails to recognize (or recognizes but fails to fix properly) is often blamed on the ECM. I have had people blame the ECM for everything from bad valve timing to CB radio interference. Here is a hint: if there isn’t an electrical solenoid or sensor involved with the system having the problem, then the ECM has no control over that system and you’re barking up the wrong tree!

From time to time, ECMs do fail. ECMs have a limited lifespan. All ECMs have some sort of flash memory and, over the years, this memory will deteriorate and ECM-related circuits on the truck will fail. Also, some ECMs rely on a battery that powers the memory chip, and when the battery wears out, your ECM will soon fail. Sometimes you will get a “check engine light” and sometimes you won’t. However, the ECM will almost never leave you stranded. Once a problem begins to develop, you will have a warning, and then several days of driving time left to get to a shop. These batteries usually last about 10 to 12 years, but we recently had a 2005 Cat Acert in the shop and the ECM had failed. So, occasionally, they will fail before their time. This ECM was only six years old and needed to be replaced. Reprogramming an ECM that is about to fail or has other hardware problems is not the answer – it will not fix the issues.

In the trucking industry, technicians tend to take shortcuts when working on electrical problems. Instead of tracking down the source of the problem, many mechanics just start making assumptions and changing parts. It doesn’t matter whether the technician doesn’t understand how to diagnose an electrical problem or is just too lazy to do it – you are the one who’s buying the parts, so their assumptions end up costing you. These guys will typically tell you that the ECM, a sensor, a wiring harness or even an injector is faulty without bothering to test the part and verify that it has actually failed. These parts are expensive, and the technician telling you to replace these parts isn’t buying them – you are – so beware of any technician that doesn’t have a well-used multi meter sitting in his toolbox.

Electrical problems are not always easy to find – especially if they are intermittent. Some problems only show symptoms under a load, at a specific rpm or when it’s cold outside. Most intermittent electrical problems come and go with no observable reason at all. Thankfully, if your ECM does produce a “check engine light” it will log which circuit produced the problem, then you can find it. If a wire is severed or a sensor fails, the ECM only knows it’s getting zero volts back from the sensor. You may just have a dirty, loose, corroded, wet or filled with oil connector. To find out, you have to ohm out the circuit to find the break with a good old-fashioned multi meter. Diagnostic software won’t do this for you – a multi meter is the only way to be sure.

Heavy Vehicle Event Data Retrieval (HVEDR)

Electronics were introduced into heavy truck engines to control emissions, the powertrain, and monitor the status of engine operations. Some of the functions such as speed, rpm, throttle and brake status are directly applicable to the analysis and reconstruction of an accident.

The name plate on the truck e.g. Freightliner, Volvo, Kenworth, etc. does not identify the engine. If unknown, the engine can be determined from the 17 digit VIN (Vehicle Identification Number). Caterpillar, Cummins, Detroit Diesel, International, Mack, Volvo, and Mercedes Benz are the major engine manufacturers.

Heavy truck engine manufacturers use different terminology for their particular module(s). MCM, VECU, ECU etc. All refer to the same basic components. Some manufacturers use a single module bolted to the engine. Others use two or even three separate units. These can be located on the engine, frame or in the cab.

There are decisions to be made with respect to “altering” the ECM Data after an Accident.

Should the vehicle be move under its own power?

Should power be removed?

If the vehicle has already been driven after the accident , does it matter?

Should a download be attempted on a heavily damaged vehicle? If so how?

Can the appropriate circuits be repaired?

Can the module be removed and downloaded?

Does downloading alter the data?

Can the module be removed to preserve the data?

The answers vary depending on a) the particular truck and ECM, b) the type of crash and c) what happened to the vehicle/engine during and following the accident.

Many trucks have other electronics that should also be considered.

Is there data in the ABS or Stability control systems?

Does the truck have an airbag system?

Does the truck have a GPS unit and if so what type?

Does the truck have electronic logs, Qualcomm or a similar system

Does the truck have any collision avoidance systems such as VORAD?

Does the trailer have any electronic systems? If so what type?

Some areas of investigation that are unique to commercial vehicles include evaluating the condition and performance of the air brake systems, analysis and interpretation of “black box” data, and the dynamics associated with articulated vehicles.

“Black box” data associated with commercial vehicles involved in an accident is becoming more common and is proving to be a valuable tool for accident reconstructionists. There are several sources for obtaining pre-crash data from a commercial vehicle; the most common source of data comes from the vehicle’s Engine Control Module (ECM). Beginning in the late 90’s, manufacturers starting incorporating the ability to access the ECM for data analysis after an incident; currently every major manufacturer supports ECM data downloads for newly manufactured vehicles. It important to note that the ECM recording capability was developed primarily as an aid to service and maintenance personnel and was not originally intended to be used as an accident reconstruction tool. As such, the data recorded by each manufacturer’s ECM does not follow a standard protocol, which results in potential pitfalls and misinterpretation by inexperienced reconstructionists.


Frequently Asked Questions
Jack Mears & Associates

1. What is a Black Box?

A Black Box, also known as an Electronic Control Module (ECM), is a device that controls the engine as well as monitor sensors on the vehicle. In addition, the ECM is capable of providing numerous reports regarding accident reconstruction such as Hard Braking & Quickstop incidents, Last Stop, and several months of daily usage reports. A new term EDR, (Event Data Recorder) is now also appearing in automobiles and trucks.

2. Are Black Boxes required on commercial vehicles?

The features used for litigation are not required on commercial vehicles but all diesel engine vehicles built today are run by an ECM. The brand of engine will determine what is available regarding litigation information. However, Black Boxes are not required on commercial vehicles.

3. How do I know if the vehicle has an ECM?

All trucks equipped with DaimlerChrysler Powersystems’s Detroit Diesel engines since 1995 have some form of electronic controls, and all Detroit Diesel engines since December of 1997 have the reconstruction information available. Mercedes-Benz engines since 2003 have the same information as the DaimlerChrysler Powersystems’s Detroit Diesel engines. All other manufacturers have had ECMs on the engine since the early 1990’s and the information that is retrievable has value in accident litigation.

4. Who can extract the Data from the ECM?

Any authorized truck or engine dealer can extract data from their own products; however, most dealers are leery to testify under oath regarding this information. There are persons in the United States who can now offer a download but, the ECM Team was the first (2001) trained, certified and dealer notified by DaimlerChrysler Powersystems’s Detroit Diesel. Caterpillar, Mack and others are now part of our services offered.

5. As an attorney, how can this information help my case?

This information can be extremely crucial for both plaintiff and defense. In most cases it is possible that the reports generated can show conclusive information determining fault in an incident and since the information generated is factual, the evidence is often used by law enforcement for accident reconstruction.

6. Can a damaged ECM still have information that can be used?

In many cases, damaged ECM’s can be downloaded. In cases where the ECM has suffered massive damage, the chip that stores the data can sometimes be removed and installed onto another ECM and allow a download to be performed. In cases where extreme fire damage has occurred there is usually no solution.

7. Is extracting ECM data costly?

While data extraction is not inexpensive, the value of the data can be priceless in litigation. ECM data could show conclusively whether or not a party is at fault or if information has been erased to limit exposure. What is the price of “Not Knowing?” In a recent case a trucking company reached a mediation agreement settling a $155 million lawsuit involving a fatality, $55 million for compensatory and $100 million in punitive damages. The settlement prohibited the disclosure of the terms. One other case was still pending when this case story hit the press.

8. How long does it take to extract and process the information?

The data extraction takes roughly 15-20 minutes and the analysis and report generation approximately one day. Turn around time on an extraction and report is 48 hours if required. We generally have the capacity to travel within four hour’s notice and in some cases can extract on the same day of an incident.

9. Can the ECM be removed from the engine and still be downloaded?

Yes, we can perform downloads of Detroit Diesel, Caterpillar, Mack, and Mercedes as well as others, with specialized tools. But we strongly suggest on-site downloading to prevent any future credibility questions arising.

10. What action should I take when it appears that an ECM download is necessary?

In the case of a fatality no one should attempt to download the ECM data. The normal tendency of the fleet is to want to see the information. We suggest that you do not allow anyone to perform a download. Most fatality cases the attorney will want to have a third party, not the fleet dealer, engine manufacturer or accident reconstructionist be involved. It is just cleaner.

11. Can I move the truck?

No, there are times that driving the vehicle and stopping quickly at a stoplight or in the parking lot can alter the last Hard Braking events or Quickstop events. Yes, if less than a certain MPH on certain manufactures, the data will not be altered. Play it safe in an all fatality type accidents.

12. Do all the engine manufacturers have the same data?

The answer is no. They each have their own type of data. Caterpillar has Quick Stop information that may be enabled or disabled. Mack and others have similar data and Cummins at this time has no surface data but some information may be helpful. In most cases there is data that could be necessary for the offense or defense in any case.

13. Who owns the data?

Clearly the owner of the vehicle. California passed the nation’s first Black Box Privacy Law protecting the privacy of drivers and companies. It took effect on July 1, 2004. It forbids access to the data without either a court order or owner’s permission. We suggest written approval.

14. Can the State or local police have access to the data?

Yes they can, but it has to be by court order and generally it is not a problem to obtain the courts approval to obtain the data.

15. Is there anything I should do to protect myself?

The answer is yes. Do not let your shop download the ECM, do not let any unauthorized individual or shop attempt to download the ECM, and do not move the vehicle. Call the ECM Team.

16. What if I have to move the vehicle?

If you do have to move it, ensure that no panic stops occur. The last stop record will change if you move the vehicle over a certain speed.

17. What if I need to operate the truck?

In most fatalities the vehicle will be impounded and inoperable. In cases where the vehicle has minor repairable damage and there is a likelihood of litigation, it would be in your best interest to have the ECM Team representative immediately download the information or remove the ECM and secure it for future potential litigation.

18. If I remove it from the engine is there anything I should know?

Most engines have an ECM mounted on the engine. In the case of Mercedes and Mack Engines there are two boxes to remove, one on the engine and one in the cab. Both are needed for a download. Check with us or your vehicle manufacturer.

19. I need information on a specific day last year; is it available?

Generally the answer is no, not on a specific day. Once the vehicle is driven after the event, the ECM only holds a certain amount of event data. The questions are what data in the ECM would have value in the case, and what trends and what information could be taken from the life to date histograms that are retained in the ECM.


Forensic Engineering Expert Witness Blog

Electronic Crash Data in Heavy Trucks and Buses

Accidents involving heavy vehicles can result in large injury and damage claims. The key to resolving these claims efficiently and fairly may be contained in one of the many on-board computer modules found in modern vehicles. The electronic engine control module, or ECM, is the most common source of electronic crash data in heavy trucks and buses. Data can include speed, engine RPM, throttle, brake and clutch use for up to a minute before a crash and 15 seconds after. This data can shed light on key questions like whether a truck was being driven at an appropriate speed and in an appropriate manner before a crash or whether the driver responded in a reasonable way to an emerging hazard.

It is best to download ECM data soon after a crash because driving a truck, or even powering it up can alter crash data. Retrieving the data in a way that will withstand the tests of litigation requires expertise. Often a complete download requires two pieces of software; one used by fleet managers and another for service technicians. Relying on either of these parties can result in an incomplete download. It is also important to document the accuracy of the ECM clock and note certain truck features so that crash data can be correctly interpreted.

If the truck is relatively undamaged, module downloads can be conducted by connecting a laptop to a plug in the vehicle cab. If the vehicle electronics are badly damaged, then the ECM must be transplanted into an identical truck or a physical connection must be made directly to the module. Both of these methods introduce risk of erasing or overwriting data and should be performed by an expert.

Once crash data has been downloaded it can be tempting to rely on it at face value. However, due to some significant limitations it should be interpreted along with the physical evidence traditionally relied on by forensic engineers like tire marks and vehicle damage. Speed values, for example, can be incorrect if certain calibration values programmed into the ECM do not match the actual truck features, or the truck’s drive wheels were sliding on the road. Both of these inaccuracies have the same root cause: the ECM calculates the speed of the truck based on information from a sensor that measures how fast the truck’s driveshaft is spinning. This calculation relies on programmed calibration factors and is only accurate if the drive wheels are not slipping on the road (due to heavy acceleration, braking or yaw.

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