Your Complete Guide to Electronic Control Modules (ECM) in Your Truck

Posted on 18 January 2019 by Tony Santos

If you drive a truck, then you are familiar with the ECM or Electronic Control Modules as they control nearly everything in your truck. If a warning light shines on your dashboard, that is the ECM talking to you and tell you something needs attention. But, it is no longer easy to fix those problems with a few wrenches and screwdrivers. Now, you need to understand how to work with electronics in order to take good care of your truck.


What is an ECM?

Many describe the ECM as the brain of the truck as it functions like a nervous system, feeling out the engine, the electricity, the controls, the drivetrain, and so much more. All parts of the truck have sensors and solenoids that travel to and from the ECM. The sensors read resistance, voltage, pressure, electromagnetic fields, and more. The sensors come in a variety of shapes and styles so they can best fit in tight spaces. They send signals about those readings to the ECM, which has a complicated little circuit board inside of it.

Then, the ECM returns the favor by sending a signal back to the sensor to make adjustments or to maintain the status quo. If something goes wrong in those messages, then you get a light on your dashboard. To understand why the light is on, the ECM will provide a code, so you or the technician working on your truck knows what to check and possibly fix.


Data that flows through an ECM

Like a typical computer, ECM uses different types of memory: RAM (random-access), ROM (read-only), and PROM (programmable read-only). ROM is programmed into the ECM and is readable by the ECM only. RAM is always changing and is sent by the sensors and solenoids. RAM requires battery voltage, or the data will be lost. PROM is programmed by the factory or manufacturer so the ECM is calibrated for the individual vehicle’s specifications. The memory chip that includes PROM can be removed and installed in a new ECM if the ECM needs to be replaced, but some ECMs do not have removable chips so the entire unit has to be replaced and reprogrammed.


What do they monitor?

As engines and ECMs continue to evolve, they have become extremely specific. Interestingly, most truck manufacturers do not use the same brand of ECM, so a Volvo truck could easily have a Cummins ECM. Each ECM is customized for the model of the truck and the sensors can be updated as necessary. Each manufacturer has special requirements for sensors and ECM systems. As standards – like emissions and fuel economy – are changed by government officials, technicians can adjust existing systems to fit those needs so trucks can pass inspections.

ECMs can be in charge of vital systems like the engine, drive train, and cabin circulation. Some are responsible for continuously checking the air pressure in every tire. Some are responsible for controlling electric windows and adjustable mirrors. Trucks also have ECMs that look at the roll and yaw of the truck and the ability of the brakes to do their job. These machines are incredibly complex and involves data points that would blow the mind of statisticians. In fact, every vehicle made after 1996 has thousands of signals running through the car at any given time.


What if something goes wrong?

Usually, the modules will tell drivers when something is wrong with their trucks. But, there will be time when the modules themselves will go bad. When this happens, the truck will not run correctly. The first sign of a bad ECM is the engine light will come on. After that, the stall or misfire, which can be rather shocking in a big diesel truck. If this happens, it is important to get the ECM checked immediately.

Since ECMs control fuel injection, a bad ECM in that area can affect the performance of the engine. Acceleration or power might be affected and fuel efficiency might drop off dramatically. Each time you start your truck, the ECM recalibrates based on the status of the weather, the altitude, and other exterior data points. Since the ECM dictates how much fuel the engine needs at any given speed and RPM, you might find that too much is being used and that can cost you a pretty penny. In these situations, it is also important to have the ECM checked before any serious damage is done to the truck.

In most situations, when an ECM goes bad, it cannot be repaired. They usually need to be replaced. Most mechanics do not have the ability to repair them, but most know how to replace them. If you prefer to have someone repair the ECM in your truck, it is important to understand the process – because it is complicated, because it is more like a motherboard in a computer than a cylinder in an engine. One of the easiest ways to know whether it needs to be replaced or not is if it smells like burned metal, from electrical damage.


Routine maintenance saves money

There will be some situations where the best move is to clean the sensors. Considering that some sensors are responsible for reading airflow, acceleration, pressure, and temperature, it is likely that the air and liquids that need to be analyzed will make the sensors dirty. Not to mention the simple fact that engines and drivetrains pick up dirt from the road. Most sensors should be cleaned on a routine basis, every few months or so. It’s much less expensive to run routine maintenance on sensors than to replace them.

If you have modified your truck, there is a chance that the ECM might not be capable of handling what you’ve done. For example, if you have a security system on your truck, it might need to be connected to the ECM so the security system can have access to some of the sensors. A cheap modification might bypass the ECM, but since the ECM controls everything on the truck, bypassing it could create problems.


Categorized | Car Tips

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