What is ECU in a car and where is it located

ECU (electronic control unit)

Electronic control unit in a disassembled state

ECU – abbreviation of the term “electronic engine control module” in English sounds like Powertrain Control Module, it is one of the main parts of the engine control system of the vehicle. This unit is often called the “brain” of the engine control system. ECU receives and processes the incoming information from most of the sensors of the car and, operating with the collected data, determines the control action on most of the control systems.

The process of reading and resetting errors ECU on Nissan Tiida

The process of removing and installing ECU on Audi 100

Diagnostic process of ECU for Daewoo Nexia

ECU placement on VAZ cars

Advantages of electronic engine control unit:

  • Optimization of engine power and torque;
  • optimisation of fuel consumption and composition of exhaust gases;
  • optimization of other internal combustion engine options.

The basic principle of operation of the engine control unit

The device is designed on the principle of combining software and hardware of the device. The main component of the hardware can be called a microprocessor, which processes analog signals from the car sensors. In some cases, the on-board unit provides the hardware impact made by the joint processing unit.

Control unit software modules:

Functional . Receives and processes signals from the sensors, and provides control actions to individual devices in the vehicle.

Controlling . Performs checks and corrects signals. Most ECU’s are programmed devices so that the user can reprogram the device at any time. This function is particularly relevant for those who have decided to engage in engine tuning: install a turbine and hypercooler, make changes in the fuel system or install additional equipment for additional fuel treatment.

The functions performed by the electronic engine control unit:

  1. Optimizing, adjusting and controlling fuel injection;
  2. Adjustment of the choke position at any stroke;
  3. Optimisation of the systems responsible for ignition, preventing ignition-related malfunctions;
  4. Exhaust gas regulation and management of exhaust vapor collection systems;
  5. Advanced regulation of most gas regulating systems and control of gas distribution;
  6. Regulation of the temperature of the cooling fluid.

The electronic engine control unit is connected to and works in conjunction with all of the vehicle’s electronics.

The main signs of problems with the electronic control unit:

The process of ECU diagnostics for malfunctions

The ECU should be replaced only after a thorough diagnosis and determination of the cause of the malfunction.

  • Absence of signals responsible for control of engine systems and actuators;
  • lack of response to regulation of the vehicle sensors;
  • complete absence of any communication with the connected diagnostic device;
  • physical damage to the ECU.

The main causes of malfunctions in the ECU:

  • Interference in the electronic systems of the car by an unqualified worker;
  • “Cigarette lightering” with the car’s engine running;
  • Incorrect connection of car battery polarity;
  • Removing the battery terminal with the engine running;
  • Starting the starter with the power bus disconnected;
  • Electrode contact with sensors or wiring during welding work;
  • Excessive moisture, which will cause water to enter the ECU;
  • Faulty ignition system parts;
  • Short circuit or partial breakage of car wiring.

ECU Repair

Only basic internal fault codes can be determined in service conditions. The unit can not be repaired, it is replaced as a whole.

You can make an independent search for faults by following a universal algorithm:

  • visual inspection of the electronic engine control unit;
  • scanning with special equipment;
  • check the serviceability of the unit by replacing it;
  • monitoring of the on-board unit operation functions;
  • full check of the on-board unit operation functions.
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Before carrying out a visual inspection or replacement you must make sure that:

  1. there is no fuel in the gas tank;
  2. there is no fuel in the fuel tank; – there is no plug in the exhaust pipe;
  3. the battery terminals are tightened securely;
  4. the car’s electrical wiring is intact;
  5. the ignition key is genuine.

One important point should be noted – when you change the control unit, the main work is to connect to the wiring through the appropriate connectors. Connection is often complicated and difficult to access the location of the ECU.

It is necessary to remember that in any case before you connect the block it is necessary to disconnect the terminal from the battery, otherwise the probability of failure of the electronic unit is very high.

And together with it, the consequences will affect the work of the power supply, transmission, exhaust system and other elements. Since the ECU needs signals from all the sensors to function properly, it needs normal battery voltage, a good ground connection, and the ability to send control pulses and signals to all the actuators in the electronic system.

Frequently Asked Questions

What is an ECU?

ECU stands for “electronic control unit”, which is the brain of a modern car that is controlled by electronic sensors. It is a block with data buses between the sensors and the control controller.

What’s inside the ECU?

Inside the metal case ECU is a board, it is the controller which stores the firmware with the algorithm of work. There is nothing else there. On the board is a processor and a device permanent and RAM. The housing is equipped with pins for information input and output signals.

How does the ECU work?

The ECU receives data from a huge number of sensors and systems of the car, processes them according to predetermined algorithms and, based on the received information, gives signals to the controlling electronics. This is how the operation of the engine or other systems is regulated. In the engine, the ECU is responsible, for example, for controlling the injection and ignition systems, adjusting exhaust gases and other settings.

Where is the ECU located?

The ECU can be located in different places, depending on the design of the car – either in the underhood space, or in the cabin, behind the torpedo and even in the trunk of the car. It is a small metal box with two large connectors.

What is ECU, where is it located in the car and what functions does it perform?

Modern cars increasingly resemble a solid tangle of wires, sensors and all kinds of computers. The car is full of electronics. We can argue about whether it is bad or good endlessly.

VAZ 2110 engine ECU

Here, it is much more important to deal with the device that actually directs and controls the work of all the electronic stuffing of the vehicle. And here we are talking about the electronic control unit, or simply ECU.

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Only the laziest person who is not interested in cars and has never penetrated into the essence of their device has not heard of this abbreviation, but there are very few of them. The majority knows about this block. To be more exact, about its existence. But they poorly imagine the ECU essence, its functions, capabilities and even location in the structure of the car.

What controls

The deciphering became quite clear and known for all. It became much easier to understand the meaning of the device even after this step. Now you know what the abbreviation is and how the ECU we are considering is deciphered. Quite often only the abbreviation is used in the technical documentation, as there is no sense for motorists to be reminded of its meaning every time. ECU may be called briefly with an abbreviation, to use the full concept of an electronic control unit, or just a controller. The essence will not change in any way. It is much more important to know what ECU is and where it is located in the car.

The internal combustion engine of the car

In fact, the block is the brains of modern car, without it we would get a pile of metal with all kinds of sensors, wires and electronic devices, not connected with each other in any way.

The ECU is almost constantly in operation mode, since it receives a huge amount of information from all sorts of sensors. This data is processed by the unit, using the algorithms provided in its program, after which it sends command signals to the so-called actuators. The unit makes pumps, ignition systems, injectors and many other things work in an appropriate mode.

As a result, it turns out that the unit acts as a manager for all electronic processes provided for in the vehicle. And this is from the elementary work of the headlights to the management of the security systems.

There is a fairly extensive list of sensors, from which the information first goes to our ECU, and then, after processing, the unit itself sends commands to the executive devices, depending on the analysis of the information received.

Among the main sensors that depend on the controller, you can distinguish several. They are responsible for:

  • motor temperature;
  • idle speed;
  • fuel supply;
  • oxygen supply;
  • ambient temperature;
  • anti-lock braking system;
  • stabilization system;
  • anti-skid;
  • speed;
  • current throttle position;
  • accelerator pedal level;
  • crankshaft; ;
  • coolant level;
  • brake fluid level;
  • on-board line voltage;
  • power steering;
  • electric power steering;
  • air conditioner;
  • heating, etc.

But here is listed only the basic set, which is almost on every modern vehicle. On more advanced cars with rich equipment, the list increases significantly.

Having processed the information received, the controller or the brain of the car sends commands to various executive units, systems and mechanisms. This makes it possible to make changes in operation:

  • the throttle valve;
  • air supply system;
  • ignition;
  • the timing of the throttle; the ignition; the timing of the throttle;
  • air conditioning system;
  • exhaust system;
  • lighting;
  • windows;
  • heating;
  • automatic transmission, etc.
Charger Protector

But even here we are talking only about the minimum set, typical for the basic configuration of an inexpensive foreign car. Increase the configuration or buy a more modern and advanced car with more electronics, and the ECU will send commands to a whole range of additional systems, mechanisms and devices.

For many, it’s amazing that one small unit does such a complicated job. And it does it all the time, without interruption, while simultaneously processing a huge amount of information.

Because of the wide range of functions and capabilities, some believe that ECU should look like a computer, laptop or tablet, have an impressive size. The only exception is the absence of a screen. But in reality, everyone is even more amazed when they see the real form factor of this control unit.

What it looks like

In fact, you already know what an ECU is in any modern car. It is the control and command center of the entire vehicle. All of the electronics used are tied to one unit. It is obliged to report to the ECU every second and sometimes even more often. At the same time, the controller itself, analyzing the received data, can correct the work of systems and the whole car, transmitting the necessary command signals to the executive devices.

Engine ECU Bosch

Now it is worth to look at the unit simply as a constituent element of the car. It is a small device, which is enclosed in a special case. The material used for the housing is plastic or metal, most often aluminum because of its immunity to corrosion.

The housing is installed in different places, depending on the specific brand and model. At the same time, the material of the ECU housing itself depends on the location. If engineers decided to install it in the cabin, then plastic and durable polymer is used, as there is no threat of rapid wear and damage. When the ECU is located in the underhood space, it is better to use metal.

Inside this body is the board. It is the controller or control unit. Outside go connectors in the number of 2 pieces. These connectors are adapted for CAN bus type. Through them there is a connection to all the wires from the sensors and devices in the car.

Additionally, most ECU has a connector for connecting diagnostic equipment. With its help you can clean ECU brains, change software, restore basic settings, delete errors, etc.

Control unit diagnostics

Active work of the block leads to its active heating. To dissipate heat, engineers provided the presence of special fins. This is similar to the radiator cooling processors that are used in computers and laptops.

When you remove this control unit from the car, you will see in front of you a box of compact size. Approximate parameters are 30×30 mm with a thickness of no more than 70 mm. Although blocks can be different, depending on the year of manufacture, the specific car and the car manufacturer.

Internal stuffing

We have understood with the box. Now it is interesting to look inside. Under the shell, acting as a cover and protection, there is a board with an impressive size. It looks a lot like the boards that are built into a usual PC system unit.

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ECU board

There is no point in going into details of the ECU board. It is important to know that it includes two key parts. This is the memory and software.

And there are three types of memory:

  • Permanently programmable memory, or simply PPZU. It is used to store various programs and functions for the power unit operation;
  • The RAM, or RAM for short. This section of the unit’s memory is needed to handle intermediate information. In fact, here the data is processed in real time;
  • The final piece of memory is the EEPROM. Also a storage device that is called electronic reprogrammable. It stores temporary information in the form of access codes, lockout, mileage, fuel consumption, etc.

The next section of the control unit board is the software. It is divided into 2 types:

  • The most important is the functional software. This is where all kinds of information from all kinds of sensors comes in. The software analyzes the data and then sends commands for execution;
  • Another type of memory are modules or control chips. They are used to control the information received and check for errors. When the software detects an error, it tries to remove it. If this fails, then the driver sees them in the form of alphanumeric symbols. The most famous can be considered Check or Check Engine. In some cases, if the error is critical, the software blocks the ability to start the engine.

Also the software within the ECU board is well known to fans of chip tuning. Here changes are made, programs are rewritten, new algorithms are set.


It is fair to know where exactly in the car the ECU is located. In reality, the unit is located in different places. It all depends on the specific car and sometimes even the year of manufacture.

ECU of Mazda engine

There are 2 main places where automakers install the control unit during the assembly of the vehicle.

  1. Interior. Since the cabin is a fairly roomy space, you should look for it based on the manual for your car. In the case of cars manufactured by AvtoVAZ choose a place under the panel near the furnace radiator. In some cars, the unit is located under the rear couch. This is most relevant lately for premium foreign cars. There are rare cases when the unit is placed in the luggage compartment.
  2. Under-hood space. In general engineers came to a conclusion long ago that it is not the right decision to place the block under the hood. This is caused by the constant impact of dirt, water, moisture, precipitations and high temperatures. All this negatively affects the unit, even if it is enclosed in a solid and reliable case. ECU should be searched in the area of the battery, near the block with the fuses.

In practice it is not difficult to find the ECU even in the new car.

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Car manufacturers never place blocks under the panels, which are hard to remove or to access it you need to disassemble half of the interior. Usually there is one hidden panel, held on clips or 1-2 self-tapping screws. It is even easier to find the ECU in the underhood. Visually look for a box, from which a couple of stubs come off.

Experienced motorists and experts in car diagnostics strongly recommend that amateurs do not try to disassemble and repair the unit. This is a complicated device, which you have probably already understood. That’s why it is extremely expensive even on budget cars. If problems arise, the best solution is to turn to a trusted car service.


Often car owners wonder how you can check your ECU for functionality. To do this, it is not necessary to disassemble the entire unit and try to unscrew something there. You should be guided by indirect signs.

Oil in the ECU

There are several signs of ECU malfunction, which are manifested as the following symptoms:

  • The engine does not start at all;
  • all or part of the systems are blocked;
  • the engine is not running properly;
  • revolutions are floating;
  • engine revolutions drop;
  • errors appear.

Any malfunction in the ECU is extremely unpleasant, as the unit is considered to be a reliable and durable element. Plus, it is very expensive. Nobody wants to face the need to replace it. Symptoms of breakage appear only as a result of improper operation, mechanical damage or incorrect software pouring, which often happens to fans of chip tuning.

The reasons for the breakdown itself are extremely trivial. These are short circuits, moisture and water on the board, overloading, overheating, physical effects, the influence of corrosive processes.

Serious damage or burnout of the board leaves almost no chance to restore the functionality of the old control unit. That is why you have to buy a new one. And then there is the main problem in the form of high cost. If you have a budget car with a simple configuration, you will have to give not less than $300-500 for the unit on the average.

Do not be in a hurry to throw away your ECU right away. First, try to disassemble the unit and see what happened inside. Sometimes it happens that errors occur due to problems with just one small chip, corrosion has damaged some areas, or contacts are broken. Such faults are repaired with 80% probability. After such repair, ECU may serve for many more years. But it is better to give it to a good specialist for repair, rather than try to do something yourself, not having the proper experience, knowledge and skills.

ECU is the most important and integral component of any modern car. And the more electronics are used in the car, the more important the ECU is. But its responsibility is also higher. Therefore, manufacturers are extremely responsible for its creation to prevent possible malfunctions, minimize malfunctions and prevent the appearance of errors. Incredibly complex device, the appearance of which sometimes makes it hard to believe.

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