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What is ecu in toyota?

4 Answer(s) Available
Answer # 1 #

An electronic control unit (ECU) is a small device in a vehicle's body that is responsible for controlling a specific function.

Shiva Siddons
Dance Historian
Answer # 2 #

The use of the term ECU may be used to refer to an Engine Control Unit, however ECU also refers to an Electronic Control Unit, which is a component of any automotive mechatronic system, not just for the control of an engine.

In the Automotive industry, the term ECU often refers to an Engine Control Unit (ECU), or an Engine Control Module (ECM). If this unit controls both an engine and a transmission, it is often described as a Powertrain Control Module (PCM).

For the purposes of this article, we will discuss the ECU as an Engine Control Unit.

What does an ECU do?

Fundamentally, the engine ECU controls the injection of the fuel and, in petrol engines, the timing of the spark to ignite it. It determines the position of the engine’s internals using a Crankshaft Position Sensor so that the injectors and ignition system are activated at precisely the correct time.  While this sounds like something that can be done mechanically (and was in the past), there’s now a bit more to it than that.

An internal combustion engine is essentially a big air pump that powers itself using fuel. As the air is sucked in, enough fuel has to be provided to create power to sustain the engine’s operation while having a useful amount left over to propel the car when required. This combination of air and fuel is called a ‘mixture’. Too much mixture and the engine will be full throttle, too little and the engine will not be able to power itself or the car.

Not only is the amount of mixture important, but the ratio of that mixture has to be correct. Too much fuel - too little oxygen, and the combustion is dirty and wasteful. Too little fuel - too much oxygen makes the combustion slow and weak.

Engines used to have this mixture quantity and ratio controlled by an entirely mechanical metering device called a carburetor, which was little more than a collection of fixed diameter holes (jets) through which the engine ‘sucked’ the fuel. With the demands of modern vehicles focusing on fuel efficiency and lower emissions, the mixture must be more tightly controlled.

The only way to meet these strict requirements is to hand over control of the engine to an ECU, the Engine Control Unit. The ECU has the job of controlling the fuel injection, ignition and ancillaries of the engine using digitally stored equations and numeric tables, rather than by analogue means.

Precise fuel management

An ECU has to deal with many variables when deciding the correct mixture ratio.

These require a number of sensors to measure such variables and apply them to logic in the programming of the ECU to determine how to correctly compensate for them.

An increase in engine demand (such as accelerating) will require an increase in the overall quantity of mixture. Because of the combustion characteristics of the fuels in use, it also requires a change in the ratio of this mixture. When you press the accelerator pedal, your throttle flap will open to allow more air in to the engine. The increase in airflow to the engine is measured by the Mass Air Flow sensor (MAF) so the ECU can change the amount of fuel that’s injected, keeping the mixture ratio within limits.

It doesn’t stop there. For best power levels and safe combustion, the ECU must change the ratio of the mixture and inject more fuel under full throttle than it would during cruising – this is called a ‘rich mixture’. Conversely, a fueling strategy or a fault that results in less than a normal quantity of fuel being injected would result in a ‘lean mixture’.

In addition to calculating the fueling based on driver demand, temperature has a considerable part to play in the equations used. Since petrol is injected as a liquid, evaporation has to occur before it will combust. In a hot engine, this is easy to manage, but in a cold engine the liquid is less likely to vapourise and more fuel must be injected to keep the mixture ratio within the correct range for combustion.

Flashback: Prior to the use of the ECU, this function was managed by a ‘choke’ on the carburetor. This choke was simply a flap that restricted the airflow into the carburetor increasing the vacuum at the jets to promote more fuel flow. This method was often inaccurate, problematic and required regular adjustment. Many were adjusted manually by the driver while driving.

The temperature of the air also plays a role in combustion quality in much the same way as the varying atmospheric pressure.

Perfecting Combustion

Since a car engine spends most of its time at part throttle, the ECU concentrates on maximum efficiency in this area. The ideal mixture, where all of the injected fuel is combusted and all oxygen is consumed by this combustion, is known as ‘stoichiometric’ or often as ‘Lambda’. At stoichiometric conditions, Lambda = 1.0.

The Exhaust Gas Oxygen Sensor (Lambda sensor, O2 Sensor, Oxygen Sensor or HEGO) measures the amount of oxygen left over after combustion. This tells the engine whether there is an excess of air in the mixture ratio – and naturally whether there is excessive or insufficient fuel being injected. The ECU will read this measurement, and constantly adjust the fuel quantity injected to keep the mixture as close to Lambda = 1.0 as possible. This is known as ‘closed loop’ operation, and is a major contribution to the advanced efficiency that comes from using engine ECUs.

Because of the strict emissions regulations now in force, there are many other systems on an engine that help to reduce fuel consumption and/or environmental impact. These include:

Each of the above systems affect engine operation in some way and as a consequence need to be under full control of the ECU.

How does an ECU work?

An ECU is often referred to as the ‘brain’ of the engine. It is essentially a computer, a switching system and power management system in a very small case. To perform even on a basic level, it has to incorporate 4 different areas of operation.

Once the data has been collected by the ECU, the processor must determine output specifications, such as fuel injector pulse width, as directed by the software stored within the unit.

The ECU has many internal power requirements for the hundreds of internal components to function correctly. In addition to this, in order for many sensors and actuators to work, the correct voltage has to be supplied by the ECU to components around the car. This could be just a steady 5 Volts for sensors, or over 200 Volts for the fuel injector circuits.

Basic ECU function

The first stage of ECU operation is in fact power management. This is where various voltages are regulated and the power-up of the ECU is handled. Most ECUs have sophisticated power management due to the variety of components inside, accurately regulating 1.8V, 2.6V, 3.3V, 5V, 30V and upto 250V all from the car’s 10-15V supply. The power management system also allows the ECU to have full control over when it powers itself down – i.e. not necessarily when you turn off the ignition switch.

Once the correct voltages are supplied, the microprocessors can begin to boot up. Here the main microprocessor reads software from the memory and performs a self-check. It then reads data from the numerous sensors on the engine and converts them into useful information. This information is often transmitted over the CANbus – your car’s internal computer network – to other electronic modules.

Once the main microprocessor has interpreted this information, it refers to the numeric tables or formulae within the software and activates outputs as required.

Example. Should the Crankshaft Position Sensor show the engine is about to reach maximum compression on one of the cylinders, it will activate a transistor for the relevant ignition coil. The aforementioned formula and tables within the software will cause the activation of this transistor to be delayed or advanced based on throttle position, coolant temperature, air temperature, EGR opening, mixture ratio and previous measurements showing incorrect combustion.

The operation of the main processor inside the ECU and the activation of many outputs is overseen by a monitoring microprocessor – essentially a second computer that makes sure the main computer is doing everything correctly. If the monitoring microprocessor is not happy with any aspect of the ECU, it has the power to reset the whole system or shut it down completely. The use of the monitoring processor became imperative with the application of drive-by-wire throttle control due to safety concerns should the main microprocessor develop a fault.

Diagnosis of an ECU and peripherals

The complexity of implementing all of this control, all of these inputs and all of these outputs requires relatively advanced self-diagnosis capability – traditional engine diagnosis becomes obsolete. The inputs and outputs of an ECU are individually monitored by the processor, often dozens of times a second, to ensure they’re within the tolerances set in the software. If a sensor reading falls outside of these tolerances for the pre-determined period of time, a fault is registered and a fault code stored for retrieval by the technician.

Fault Codes

When a fault code is stored in the memory, it usually results in some of the logic within the software being bypassed with reduced engine efficiency, albeit with the engine still being able to function on a basic level. In some circumstances, the self-diagnosis routine discovers a serious fault that either fundamentally prevents the engine from running, or shuts the engine down in the interest of safety.

With modern engine management, the first fault diagnosis step for a vehicle technician is to access fault codes from the ECU memory. These are often stored as 5 digit alphanumeric codes beginning with a P, B, C or a U, followed by 4 numbers. Details of these codes and their descriptions can be found here: OBDII Fault Codes

In addition to these codes, the technician can also view live sensor data through the diagnostic tool while the vehicle is running. This allows them to see a sensor reading that is incorrect, but not out of tolerance by enough of a margin to flag a fault code.

Electronic Throttle Control

Many people question the necessity of drive-by-wire throttle control. Introduced in the 90s, it is now fitted to almost every engine produced today, but what are the advantages over a traditional cable?

Until the 80s, most throttle/accelerator control was managed with a cable from the pedal to the carburettor. The idle speed was set by simply adjusting a screw to keep the throttle flap open slightly until the engine idled correctly. This simple method required regular adjustment of idle speed and was prone to deviation when an engine was cold or as various parts wore out.

In the 1980s, with the mainstream introduction of ECUs, electronic Idle Air Control valves were introduced which solved many of these issues, however the ECU was now controlling part of the airflow and yet all of the other components remained.

With efficiency of engine operation and efficiency in car assembly moving forward, electronic throttle control was introduced. This sped up the manufacture of a car (no stiff throttle cables passing through the firewall), it removed the need for an Idle Air Control valve and it allowed the engine ECU additional control over the engine for improved EGR function, improved control over engine shutdown and improved starting.

One important advantage of electronic throttle control is that the ECU can adjust the throttle angle during acceleration to compliment the actual airflow through the engine. This improves the speed at which the air passes through the intake and provides gains in torque and drivability. This is known as torque-mapping and is only possible with electronic throttle control.


Modern vehicles are built to much tighter tolerances than those of the past, however they are still susceptible to manufacturing variation, mechanical wear and environmental aspects. As such, they are able to adapt to gradual changes in the operation of the engine.

Example. As an air filter gets blocked by dust, the ECU can start the engine running with a slightly reduced fuel injection quantity to compensate. This allows it to perform at peak efficiency from engine startup, rather than starting at factory levels and working towards the optimum mixture on each journey.  It does this by storing the Lambda values over previous journeys.

These adaptations apply not just to blocked air filters, but to many systems on an engine or transmission. As components in hydraulic systems wear, they require changes to the timing of solenoid activation to compensate. Similarly, as the engine wears throughout, the ability to be an air pump deteriorates slightly and the opening angle of the throttle flap will need to change to maintain correct idle speed.

How to diagnose a faulty ECU with no communications:

Dreaded P0606 fault code - is it really caused by your ECU?

Bad Camshaft Position Sensor Symptoms - and how to FIX!

The timeline of the ECU


ECUs started out simply controlling a couple of solenoids on carburetors to make them function more effectively. Some started controlling mixture at idle speeds.


With the introduction of fuel injection, the ECU took on a new role of being completely responsible for the fuel and ignition management of petrol engines.

Closed loop Lambda control was soon included and the ECU rapidly began a new era in engine efficiency.


The ECU was now handling vehicle security. It was also beginning to appear on Diesel engines, which played no small part in the success of the turbodiesel engine over the next couple of decades.

Denison Dierker
Engine Driver
Answer # 3 #

The differentiation is done depending on the tasks each unit would perform, and they are listed as below:

It is commonly used in vehicles with ABS, and BCM ensures that the wheels do not skid and helps in ease of brake management. It also prevents wheels from locking up at the time of using the brake.

It mainly controls the fuel and its ignition timing that is important to power up the engine and its correct use for driving the car.

This TCU ensures that onboard services are running correctly. It helps control satellite navigation in the car, along with internet and connectivity with phones inside the car.

It is connected with your vehicle's suspension system and ensures the correct height of the suspension. It should be able to adjust with optimal changes as per changing driving conditions.

It is common in an automatic vehicle as it helps ensure a smooth shift in the car by assessing the engine of the car. It also helps in the smooth acceleration of the car.

The working of the ECU isn't that simple. The electronic device has base numbers with parameters filled in memory. There are different sensors working around ECU, and it helps in better management of electronic systems. It should help in efficient driving of the car and improve the output. Therefore, this, it helps in better handling of electronic systems.

The car has several sensors that are known as crash sensors, and it indicates the ECU about the crash. The ECU can measure the speed of the vehicle accurately when there is an accident, and using the onboard memory, it would consider whether to launch the airbags then and there or not.

If the data is accurate enough, close to accidents, it should deploy the use of airbags, and all these will happen in milliseconds, and the use of airbags can save lives. Therefore, this is how the ECU works responsively when there is a worsening condition or the car tends to break down.

Having a faulty ECU is the worst thing to happen in a car, and it will heavily impact the car's overall performance. There will be a drop in fuel economy and other changes in thevehicle during gear shifts. The engine light would stay on, indicating there are certain errors resulting from minor to major in the car system.

However, when the ECU is not working anymore, the start would not start, and it controls the engine ignition. In addition, other features will stop working as the engine cannot be started at that point. This is where one should understand the correct functioning of ECU for smooth car driving.

As vehicle manufacturers continue to add additional functions and features to the car, space tends to become an issue. Each feature requires supportive ECU, and so, there should be an adequate incremental approach to help drive the car smoothly.

French Deak
Answer # 4 #

An engine control unit (ECU), also called an engine control module (ECM), is a device which controls multiple systems of an internal combustion engine in a single unit. Systems commonly controlled by an ECU include the fuel injection and ignition systems.

The earliest ECUs (used by aircraft engines in the late 1930s) were mechanical-hydraulic units, however most 21st century ECUs use digital electronics.

The main functions of the ECU are typically:

The sensors used by the ECU include:

Other functions include:

In a camless piston engine (an experimental design not currently used in any production vehicles), the ECU has continuous control of when each of the intake and exhaust valves are opened and by how much.

One of the earliest attempts to use such a unitized and automated device to manage multiple engine control functions simultaneously was the created by BMW in 1939 Kommandogerät system used by the BMW 801 14-cylinder radial engine which powered the Focke-Wulf Fw 190 V5 fighter aircraft. This device replaced the 6 controls used to initiate hard acceleration with one control, however the system could cause surging and stalling problems.

In the early 1970s, the Japanese electronics industry began producing integrated circuits and microcontrollers used for controlling engines. The Ford EEC (Electronic Engine Control) system, which utilized the Toshiba TLCS-12 microprocessor, went into mass production in 1975.

The first Bosch engine management system was the Motronic 1.0, which was introduced in the 1979 BMW 7 Series (E23) This system was based on the existing Bosch Jetronic fuel injection system, to which control of the ignition system was added.

In 1981, a Delco Electronics ECU was used by several Chevrolet and Buick engines to control their fuel system (a closed-loop carburettor) and ignition system. By 1988, Delco Electronics was the leading procuder of engine management systems, producing over 28,000 ECUs per day.

Such systems are used for many internal combustion engines in other applications. In aeronautical applications, the systems are known as "FADECs" (Full Authority Digital Engine Controls). This kind of electronic control is less common in piston-engined light fixed-wing aircraft and helicopters than in automobiles. This is due to the common configuration of a carbureted engine with a magneto ignition system that does not require electrical power generated by an alternator to run, which is considered a safety advantage.

Havana Schuck
Chief Analytics Officer