Table of Contents

Summary

  • ECU is an acronym for Electronic Control Unit, and is also known as the brain of a car because it controls all of the electronic components in a car.
  • If your car has a bad ECU, it may cause the engine to stall and misfire, lack power, acceleration, and ignition pulse.
  • You may also experience poor fuel economy and rough or irregular shifting.
  • Sometimes you may notice your car not starting, showing a check engine warning light, or smelling inside like electric burning.
  • Short circuits, vibration in the car, corrosion, excessive temperature, and irregular voltage are the issues that may cause your car’s ECU to fail.
  • Methods like visual inspection and running a diagnostic test by using a code reader can be employed to confirm if your car’s ECU is bad or not.
  • After doing above mentioned diagnostic methods, if it turns out that your car’s ECU is bad or faulty, you may have to bear the cost of repairing or replacing it, which ranges from $500 to $1000, on average, for repairing and $1000 to $3000 for replacing the ECU.

Role of ECU in Cars

The presence of electronics in cars did not grow overnight; it took decades to reach the level they are at today.

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The first ECU was introduced around 1978. The installment of ECUs in cars has completely evolved the automobile industry, as modern vehicles can now integrate up to 150 ECUs to give you as much ease as possible.
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ECU is an acronym for Electronic Control Unit and is also referred to as the engine control module (ECM). It is an electronic device known as the brain of a car because it controls all of the electronic components in a vehicle by receiving signals from multiple sensors.

It performs different jobs, including managing the engine performance, fuel efficiency, and stability of the car; for example, it controls when the fuel injectors open and close. It also regulates how much fuel should be in the air/fuel mixture. Therefore, it is of key importance to track your car’s ECU performance, as a faulty ECU may cause your car to suffer many problems.
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Let’s find out what are the symptoms of a bad ECU.

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Symptoms of a Bad ECU

If you suspect your car has a bad ECU, here are some symptoms to look out for:

1. Engine Misfiring or Stalling

A bad ECU can cause the engine to stall or misfire. It is because the ECU controls the fuel and air intake and the timing of these functions. A faulty ECU may not be able to adjust these settings properly, which results in misfiring or stalling.

2. Sluggish Acceleration & Lack of Power

The ECU is the computer that controls the engine and transmits all the data to other parts of the car. It is a critical part of cars and can affect performance. For example, it controls the fuel injection system by regulating how much fuel should be injected into the engine at any given time. It also monitors sensors that tell how much air and fuel are in the engine and adjusts accordingly.

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A bad ECU cannot perform these functions accurately, and resultantly, the engine fails to get a perfect mixture of fuel and air. Eventually, your car will suffer sluggish acceleration and lack of power.

3. Apparent Loss of Ignition Pulse

The ignition system is responsible for turning the fuel into energy that powers the engine. The ECU controls the timing and duration of each spark, which in turn determines how much energy is delivered to the engine. If there is a problem with the ECU, it may not be able to deliver enough energy to ignite all of the fuel in time, leading to a ‘‘loss of ignition pulse’’.

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This can also be caused by many factors, including a clogged air filter or dirty fuel injectors.
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4. Poor Fuel Economy

The ECU is responsible for monitoring the engine’s performance and adjusting the parameters to keep it running smoothly. It also monitors the fuel mixture, temperature, and other factors that impact the engine’s performance. A bad ECU can cause a loss of fuel economy because it will not be able to adjust parameters properly or monitor any changes that may affect its performance.

5. Check Engine Warning Light

When the engine warning light turns on, there is a problem with the engine. The light could be turned on due to a bad ECU or a faulty sensor as they fail to assess the situation rightly and trigger false alarms.

6. Electric Burning Smell

An ECU can sometimes cause an electric burning smell if it is faulty. For example, it could be due to electrical shorts, a blown a fuse, or a cracked solder joint. Sometimes burn marks can also be seen in the ECU.

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You may also experience an electric burning smell due to short circuits caused by messy or bad wiring.

7. Car Won’t Start

If your car engine shuts off for no reason, it could be because of a bad ECU. This can happen when the ECU needs to be calibrated properly or when the ECU needs to communicate with the other components in your car [3].

8. Rough or Irregular Shifting

Your car’s transmission is mainly responsible for shifting gears. In modern cars, transmissions are controlled and regulated by a computer called TCU (Transmission Control Unit). TCU mainly relies on ECU for its work. Nonetheless, when a faulty ECU sends inaccurate data to the TCU, it shifts the gears according to that information, and thus, the car experiences rough or irregular shifting.

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Causes of ECU Failure

1. Short-Circuit

A short circuit can cause an ECU to fail. A short circuit happens when electricity passes through wires or other components in a way that it should not, such as when there is too much electricity or limited insulation.

2. Vibrations in the Car

Vibrations in engines or other mechanical systems can cause damage to the ECU. ECU is made of many components, such as microprocessors and transistors integrated with the help of soldering. Recurring or constant vibration causes breakage between these components. Consequently, ECU stops working appropriately.

3. Temperature

Increased temperature yields flawed ECU because the sensors in the ECU can get damaged by high temperatures. Therefore, the higher the temperature, the higher the chances of a faulty ECU.

4. Corrosion

There are many reasons why the ECU may be faulty, but the most common reason is its exposure to water or other liquids. The water can cause corrosion of components in the ECU, leading to an electrical short, which causes your car’s engine to shut off for no reason. You should also check that your battery terminals are clean and not corroded. Due to corrosion, ECU may not get the required voltage and fail to perform skillfully.

5. Irregular Voltage

Voltage surges, power outages, and electrical shorts may cause an ECU failure, as it requires 12 volts to work properly. Therefore, inappropriate voltage disables the proper functioning of the ECU.

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How to Diagnose Problem in ECU?

If you want to check whether your ECU is working properly or not, perform the following tests:

Spotting the Issue by Visual Inspection

Inspection can be done by looking for traces of short-circuit, corrosion, or burning inside the ECU. If these areas appear in order, wires coming from the battery towards the ECU should be checked for short-circuit or lost connection.

Run a Diagnostic Test Using a Code Reader

A diagnostic test can be run using a code reader. If the code reader fails to communicate with the ECU, it means there is some problem going on with it. If the problem is with some other part of the engine or transmission and not with the ECU, it will show some error codes. These codes are distinct from each other and signify different problems with the car. A code reader is an essential diagnostic tool for all car owners. It can help identify problems with your car, and it can even tell you how to fix them.

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Cost of Repairing/Replacing ECU

The cost of fixing a car’s ECU problem may vary depending on the location and the car’s make or model; however, an average price is listed below in the chart.

Methods of Fixing ECU ProblemAverage CostAverage Labor Cost
ECU Inspection–$150 – $300
ECU Repairing$300 – $750$100 – $200
ECU Replacing$1000 – $3000$85 – $108

Conclusion

The ECU is a computer that has been integrated with cars for decades. It controls everything from regulating the engine and how much fuel to use to when and how fast your car can accelerate. The ECU can be programmed for many different tasks, but it’s not infallible. A car’s engine might not work properly or when it malfunctions. If you notice any of the above symptoms, get your car to the mechanic without any delay to save yourself from the hefty costs of replacing the ECU.

FAQs

Generally, ECUs of those vehicles which predate 2001 can be replaced by yourself because they do not demand new programming. However, the ECUs of modern cars cannot be easily replaced as they require reprogramming. Therefore, it is recommended that you should always take your car to a certified technician to replace ECU because they are experts.

If you are noticing any of the following symptoms in your car, it may be having a failing ECU. Check engine light; · Engine stalls; · Poor fuel economy; · Decrease in engine performance; · Car doesn’t start

ECUs of well-maintained cars are seen to be working perfectly even after decades past. Generally, an ECU lasts at least 100,000 miles, but it only requires a little TLC.

The purpose of an ECU Fuse is to protect ECU from irregular voltage. It, on the one hand, works as a bridge between ECU and the car’s battery, whereas; on the other hand, it provides a shield wall to the ECU. Fuses are prone to handle normal voltage fluctuation, but they get blown while encountering it in excess. When a fuse blows, the ECU stops working as it loses voltage connection. They are installed in ECUs because they are not only cheap but also easy to replace.

The ECU is responsible for monitoring the engine’s performance and adjusting the parameters to keep it running smoothly. It also monitors the fuel mixture, temperature, and other factors affecting the engine’s performance. A bad ECU can cause a loss of fuel economy because it will not be able to adjust parameters properly or monitor any changes that may affect its performance.

You may see up to 150 ECUs integrated into modern luxury cars. However, older cars used to have one ECU, whereas; modern cars usually come with around 80-100 ECUs.

About Author

Andrew Ray

Andrew is an automotive technician with 10 years of experience mainly in American and Japanese cars, covering everything from routine vehicle maintenance and engine inspections to tire rotation.