So what is an E.C.U? If you type ecu into the google search bar and you click enter. The first definition you get is “An engine control unit (ECU), also commonly called an engine control module (ECM), is a type of electronic control unit that controls a series of actuators on an internal combustion engine to ensure optimal engine performance.” Which is an excerpt from Wikipedia but if you’re opting for a more refined definition, yourmechanic.com expresses it as “The engine control module (ECM), also commonly referred to as the engine control unit (ECU) or powertrain control module (PCM), is one of the most important components found on virtually all modern vehicles. It essentially functions as the main computer for many of the vehicle’s engine performance and drivability functions. The ECM takes the information from the engine's various sensors, and uses that information to calculate and tune engine spark and fuel for maximum power and efficiency.” Please for the purpose of this article, I’ll refer to it as ECU.
As you can see, the ECU plays a very important role such as N’golo Kante’s contributions to the EPL over the last two seasons. Due to the fact that many of the essential functions are controlled by the ECU. It can cause all sorts of problems and in some cases, even render the vehicle immobile. A bad ECU will usually reveal symptoms that can alert you of its potential fault/damage.

Symptoms of a bad ECU
• The check engine light remains after resetting
The check engine light usually comes up if the car’s on board computer detects any fault or loop-sided feedback in its circuitry. Sometimes, it could display regardless of faults and this could be due to bad ECU. It is highly recommended that you diagnose properly before carrying out any replacements or undergoing any repairs.

• Faulty transmission
A bad ECU can often result in a faulty transmission especially in vehicles with Automatic Transmission. That’s why it’s necessary to check your vehicle out as not all perceived mechanical faults are entirely mechanical, it could also be electrical.

• Engine misfires or turns off erratically
Yes I know, this probably looks like a fuel pump issue but it could also be as a result of bad ECU. At the risk of sounding like a broken record, I’ll reiterate, check properly before making any decision.

• Inability to start
A bad ECU oftentimes may cause you to experience difficulty starting your vehicle. It may or may not start at all, even if or especially when the battery and electrical components are in good condition.

• Sudden drop in fuel economy
I must admit, this strongly defies car logic but apparently the ECU learns your driving pattern i.e. how you accelerate and brake. How does this affect fuel consumption? You ask, well in adapting to your driving style, the ECU could gradually increase the quantity of fuel being delivered to your engine during combustion in anticipation of an aggressive driver.

The ECU in most cases is preset by manufacturers for a particular region. That’s why it is advised, you carry out an ECU reset when you buy a used vehicle albeit this could be counter-productive as there have reports of increased fuel consumption after reset or update of ECU. When manufacturers were contacted as to why this strange phenomenon was taking place, they replied something about reducing emissions.

• Loss of power
A bad ECU can detect a non-existing error in a vehicle. Thereby causing the ECU to give a command to the engine to lose power or stop the engine completely in order to prevent an accident. It’s a fail-safe feature embedded into the system by manufacturers although it seems unnecessary.

• Reduction in engine efficiency
The efficiency of an engine could reduce due to faulty ECU relaying bad commands to the engine. Thereby causing the engine to jerk or stop every now and then. On a side note, with technological innovations propelling the automotive industry into the jet age. We may yet see an over-reliance on vehicle’s onboard computer especially with many manufacturers announcing hybrid/all electric models as upcoming launches in coming years.


Possible causes of bad ECU

• Improper battery terminal connection
This is very self-explanatory. You connect the terminal wrongly, you potentially fry your vehicle’s electrical unit albeit some manufacturers, as a fail-safe, install a battery fuse (main fuse) that’ll blow up instead of the entire electrical system. All in all, be careful whenever you insert and connect a vehicle’s battery.

• Dead battery cells/corrosion
Vehicles which predate the 90’s are commonly affected by the aforementioned issues. That doesn’t mean your new car can’t be affected, so always ensure that you clean up the terminal head whenever you notice corrosive build up. Also, if you’ve abandoned your vehicle for some time, it is suggested that you take out the battery, charge up (if it’s dead) and warm your vehicle. Ignorance of these things can lead to massive problems at the end of the day.

• Fire or water damage
We are all aware of the massive floods that happened over the course of the weekend as result of non-stop rainfall in the last two weeks. Most folks need not be told that water/fire and electronic devices don’t go well together. Again it’s advised you check your vehicle out through proper diagnostic methods for any faults before driving if you vehicle was submerged in water.

• Improper grounding
Grounding, in automotive terms is a connection to the body or metallic surface of the vehicle. Thus any connection to the body of the car is a connection to the negative terminal of the battery. Electricity flows from the positive of the battery, through the circuit to do some work, then back through the body to the battery. This is a “negative ground” system which is by far the most popular automotive ground scheme used in the automotive world.

The main reason this is done is to greatly simplify the wiring of a vehicle. Since most car bodies are made of metal, they provide a perfect ground plane, eliminating the need to run a separate ground wire to each circuit which reduces the amount of wires necessary in half.

Good grounds are important because poor grounds cause voltage drop. The consequence of this voltage drop is that the systems in that circuit can malfunction and this is likely to affect the ECU.


Solution to repair or replace ECU

From everything that’s been said, we hope you’ve realized how important the ECU of a vehicle is as it basically the engine’s brain. If you suspect a bad ECU in your vehicle, make sure you take your vehicle to a mechanic or garage that uses latest computer diagnostic equipment to check your vehicle’s onboard computer.

I hope you have been educated by this piece. Once again, the need for proper and thorough diagnostic can never be over-emphasized. We wish you well. Have a good one.

Very educative

Coolgent:
Very educative

Thank you fine Sir(I presume). We aim to please!

LadipoNG:

Thank you fine Sir(I presume). We aim to please!

Can a car accident damage the ECU as well?

Check this thread https://www.nairaland.com/6097483/power-new-engine-old-engine

Thanks OP,
Exactly the challenge I'm experiencing with my Toyota Carina E