Your car’s engine control module (ECM) acts like the brain of your vehicle. This module controls nearly every aspect of your car’s engine, including the engine timing, ignition firing, and other systems. It even plays a role in controlling the shift points of your transmission.
You might also hear the ECM called the ECU, or engine control unit. When this module goes bad, it can wreak havoc on your vehicle. You might find that your car won’t start, you experience engine misfires, or there are strange happenings with your electrical system. Sometimes an ECM can be repaired, while it might need replacement in other cases. Keep reading as we give you all the details on how an ECM works and how to determine the best way to fix it.
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What Is An ECM & How Does It Work?
The ECM in your vehicle is a small computer that controls many systems in your vehicle. The ECM is a type of electronic control module that controls these systems by sending signals to various engine components. The engine control module constantly monitors data from many different sensors inside the engine bay and the engine itself. For instance, the ECM is constantly monitoring the airflow through the mass airflow sensor as well as the position of the camshaft and crankshaft. The ECM also monitors input data from oxygen sensors, coolant temperature, engine temperature, and various other data points.
Using the data collected from these sensors, the ECM makes decisions about how the engine should operate. Your car’s manufacturer has programmed the ECM to make these decisions based on the available data. For example, the ECM might use the data from the crankshaft and camshaft sensors, along with engine RPM data, to determine when to fire the ignition system. The engine control module processes a large volume of data very quickly to make your engine run as efficiently as possible.
Symptoms Of A Faulty Engine Control Module
So, how do you know when your engine computer is having problems? Since the computer controls so many different aspects of your vehicle, problems can appear in a number of different places. Here are some of the most common signs that you might have a faulty ECM.
— Engine Misfiring
The engine timing is one of the many things controlled by your engine’s electronic control unit. The unit uses data such as the engine RPM, camshaft position, crankshaft position, and throttle position to determine when the ignition system should fire. If the spark plugs fire at the wrong time, an engine misfire will occur. Similarly, if no spark is created in the combustion chamber, that will also result in a misfire condition. You might be able to feel the misfires as you drive, as they typically feel like a slight hesitation or skip in your engine. A faulty ECM could be responsible, so you should have an auto repair shop check out the problem for you.
— Check Engine Light
There are many different problems that can cause your check engine light to illuminate, and a bad ECM is one of them. You might even find that other problems related to the faulty ECM will cause the light to come on. For example, a bad ECM might lead to engine misfires. When misfires occur, the check engine light will come on. However, your car’s computer can also detect problems within the ECM itself, and it will trigger the check engine light in that case. You will need a scan tool to pull the trouble codes from the computer, and those codes might reveal an issue with the engine control module. Make sure that you use the scan tool to reset the check engine light after the issue has been corrected.
— Poor Performance
Poor engine performance can sometimes be the result of a failing ECM. Whether the ECM is incorrectly processing the data inputs or the ECM is sending the wrong outputs, your engine performance might be affected. Remember that the ECM controls the engine’s timing, and improper timing will greatly affect the engine’s performance. Dirty or clogged fuel injectors might also cause a performance problem. The ECM may be sending the proper signals, but the injectors cannot get enough fuel into the combustion chamber due to buildup. In that case, you might need a mechanic to help diagnose the root cause of the problem.
— Engine Won’t Start
In severe cases, a bad ECM might cause your engine to fail to start at all. If the circuit board inside the ECM has totally failed, then critical systems on your vehicle might not be getting any signals from the computer. This condition could also lead to engine stalling, so you might not get much warning in some cases. A bad fuel pump could also prevent your car from starting, so make sure you perform the proper diagnosis before attempting to repair or replace your ECM.
— Transmission Shifting Poorly
Most modern transmissions are generally controlled by the transmission control module (TCM) or the powertrain control module (PCM). However, these control units also get data from your engine control module when determining the proper shift points. If your ECM is bad, your TCM might be getting bad data from the engine. Similarly, it might not be getting any data at all. Even though your transmission control module might be working properly, the transmission may shift poorly if the ECM is bad. If you start to notice poor shifts, it could be due to a faulty ECM.
Should You Perform An ECM Repair Or Replacement?
Before you attempt to fix the ECM, it helps to know a little more about the cause of the problem. Most of the time, problems with the ECM are the result of software bugs. In this case, the ECM needs to be reprogrammed with new software. You often hear about manufacturers issuing software updates for their vehicles, and the dealership will need to reflash the ECM to install the new software. If your problem is related to a software issue, then you can probably repair the ECM by reinstalling the software. However, make sure that you have a skilled mechanic perform this work. If you attempt to do it on your own and fail, you have probably ruined the ECM altogether.
On rare occasions, an ECM problem is due to a hardware issue. This could be a result of corrosion, bad connections, a blown fuse, or a power supply problem. There are many repair services out there that will attempt to perform an ECU repair. Some specialize in ECM rebuilding. However, repairing automotive electronics can be finicky. Sometimes the circuit board simply cannot be repaired. For this reason, most people suggest replacing the ECM instead of attempting to repair it. Most new engine control units also include at least a one-year warranty, so you can get a free replacement if your new ECM has any issues during this timeframe.
ECM vs. ECU vs. PCM: What’s The Difference?
So, what’s the difference between all these acronyms? The answer is not as complicated as you might think. The ECM and ECU are the same things. Some people refer to this part as the engine control module, while others call it the engine control unit. There is no difference between the two. This module controls the engine by using input data from various sensors in the vehicle. Vehicles with an ECM or ECU will usually have a separate TCM or transmission control module. The TCM controls the shifting of the transmission.
Instead of using separate engine and transmission control modules, newer vehicles utilize a single module to control both the engine and transmission. This unit is known as a PCM or powertrain control module. The benefit of a PCM is that the vehicle becomes more efficient. Since both the engine and transmission are controlled by the same unit, data is shared and processed more quickly. This leads to better fuel economy, smoother shifting, and quicker vehicle response. If you experience problems with your PCM, the first step is usually to reprogram it. Similar to an ECM, most people opt to replace the PCM instead of attempting a PCM repair when there are physical issues with the part.
The Bottom Line
Your vehicle’s engine control module processes lots of data from sensors in the engine to control the engine and make it run more efficiently. Older vehicles did not have an engine computer, but all of today’s cars have them. Whether you have a Dodge, BMW, or Ford ECM, the basic function of the part is the same. Problems with your ECM can lead to engine misfires, a check engine light, or problems starting the car. Engine control module repairs are often difficult to complete, so many people simply choose to replace the part altogether when they have issues.
Frequently Asked Questions
How much does it cost to fix an ECM?
The cost to fix an ECM depends on the make and model of the vehicle. There are repair services out there that will fix your ECM for a few hundred dollars – assuming that the part is repairable. Replacement of the ECM is typically a little more expensive. On average, you can expect to pay around $1,000 for an ECM replacement. This cost could range from as little as $700 to as much as $1,500 on some vehicles.
What happens if your ECM fails?
If your ECM fails completely, your vehicle will likely not run. Failure could potentially occur during driving, so your engine will probably stall in this case. Complete ECM failure is not common, but software bugs in the ECM are more likely. In that case, you might experience engine misfires or poor performance. While the vehicle will probably still run, it will not run efficiently when there are problems with the ECM.
Is it possible to buy a used ECM?
Yes, it is possible to buy a used ECM. There are some websites that sell used ECM parts, and you might also find used ECMs in vehicles that have been wrecked. You could visit your local junkyard in search of used ECMs. Even if the vehicle was in an accident, the ECM would usually still function correctly unless the part was physically damaged. Some people choose to sell their car for parts after an accident, and you might find a used ECM this way. A used ECM can be a great option for anyone looking to save some money on an ECM repair.
Can an ECM be repaired?
Yes, an ECM can be repaired in some cases. Depending on the problem or the extent of the damage, ECM repair is often a viable option. However, it can be extremely difficult to perform a repair to the circuit board in some cases. You should always consult an expert before attempting an ECM repair. You might be better off replacing the whole unit instead of wasting time and money trying to repair it. Some mechanics will not even attempt a car computer repair.
