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Engine Control Module, its component and function

The control unit receives information from the different sensors and probes, analyzes it according to its program and governs the different ignition and injection components. It can be named as: ECC, ECM, ECU, ECCS, CPU, etc.

engine controle module

The ECU uses microprocessors to gather information, process it and send signals to the excited transistors to activate the different actuator circuits. The three main processors are RAM (temporary memory), ROM (basic computer program) and PROM (fine tuning program), these three microprocessors are the heart of the CPU.

Electronic Control Module

The electronic control module, or ECM, is the brain of the fuel injection system and is divided into the following memories: the ROM; the RAM and in some types the PROM.


 or read-only memory, is the section of the ECM that contains the main set of instructions that the computer follows. This is the section that says, “When I see this happening, I have to make it happen.” The microprocessor that contains these ROM instructions is a non-volatile chip. This means that the program designed in it cannot be deleted when power is turned off.


or random access memory, is the section that has three main functions in the ECM. The first function acts as the ECM's notebook; Whenever a mathematical calculation needs to be done, the ECM uses the RAM. The second function is to store information in the block learning multiplier (BLM) system when the engine is off or operating in open loop. The third function is to store diagnostic codes when a system fault has been detected. These codes are stored for fifty engine restarts or until battery power is removed from the ECM. Unlike ROM and PROM, RAM chips are volatile memories.


or programmable read-only memory, is the calibration section of the chip in the ECM. The PROM works in conjunction with the ROM to fine-tune the fuel control and ignition timing functions for the specific application. The PROM is also a non-volatile memory. It contains the information about engine size, transmission type, car size and weight, rolling resistance, drag coefficient and final drive ratio.

The ECU performs the following functions:


I/O gate is the abbreviation of input-output gate in which the microprocessor converts signals from various sensors into codes, and also converts the operating results into signals for the operation of the injector, power transistors, etc.


read/exclusive memory and RAM (random access memory) are the memories of the microcomputer. The ROM stores the ideal data for fuel enrichment, ignition tuning, etc., and the computer can only read these Data Memory The RAM allows the calculation results of various data sent from the sensors to be temporarily stored. Previously stored data can be deleted from this memory.


(central processing unit) is the brain of the total microcomputer system and controls the various functions of the computer. It processes the signals sent from the I/O gate while controlling the ROM and RAM, and also transmits the computed results from the I/O gate to the injector, power transistor and so on.

What is a digital control?

Another characteristic of the computer is that its control unit corresponds to a digital control system. The resistance of the cooling temperature sensor varies constantly with temperature, and this type of signal is called “analog.” In addition to this signal, the ECU uses analog signals from the air flow meter and others.

Meanwhile, the signal from the crankshaft rotation angle sensor, for example, is not continuous, it is discontinuous and is called a digital signal. Generally speaking, the digital signal represents discontinuous values from one point to another, and its precision is lower than that of the analog signal. However, precision can be increased by reducing the separation between sampling points.

  • The main reasons for adopting digital control system are as follows:
  • The control unit can control a complicated system.
  • The control unit can be made compact.

Since the signal is composed of ON-OFF pulses, the ECU operation can be limited to 0.1 operation and its combinations; This leads to reduced computing errors and good durability. In the case of analog type, the electrical noise and different characteristics of semi-conductor itself, for example, the internal resistance of the transistor, is different between the same models which can easily cause error.

In order to change the analog signal to digital, the control unit uses the AD (analog – digital) converter.


The ECU is capable of controlling various functions. It is also capable of providing more precise and sophisticated control. The functions that can be controlled by the ECU are the following:

Fuel injection control

This control is basically identical to that of the E.F.I system. however the ECU provides more detailed control. For example, a learning control system is used to maintain an optimal idle mixture ratio at all times.

Ignition tuning control

It corresponds to a new function. The optimal ignition setting is determined by receiving signals from different sensors.

Fuel pump control.

The ECU controls the voltage applied to the fuel pump and reduces the voltage applied to the fuel pump to reduce fuel pump noise and electrical power consumption at idle.

Auto diagnosis

Check whether the input and output signal systems to and from the control unit are normal.

Idle speed control

It receives signals from various sensors and regulates the engine to optimal idle speed according to the engine load.

Idle Control.

Increases idle speed when battery voltage is low, or when many charge switches are activated.

Pressure regulator control

Temporarily increases fuel pressure when the engine is started with high coolant temperature. There is another module in addition to the control unit.

Air regulator control.

In the conventional system the air regulator was normally activated with the ignition switch in the ON position. In other cases, the air regulator is activated only when the fuel pump is operating, in order to reduce electrical energy consumption.


E.G.R. control is also used. (exhaust gas recirculation), A.V.I. control. (air indicator valve), etc.


From the point of view of the function it performs, a microprocessor is responsible for executing the instructions of a program one at a time. A ROM (READ ONLY MEMORY) memory is an integrated circuit that is designed to permanently store the program and data accessed by the microprocessor. There are different types of memories that fall into this category. They work in a way analogous to a CD or video cassette, once something is recorded on them, even if the power is cut, the data recorded on said medium is not erased.

Anecdotally, PROM memory manufacturers claim that the data recorded in them remains unchanged for 20 years without any power source connected. What's more, every time they connect to their source, the data stored there is secured for another 20 years.

A RAM memory (RANDOM ACCESS MEMORY) is a memory that is designed to store data temporarily. In some ways this type of memory is similar to the short-term memory of our brain.

When the RAM stops receiving power, it loses its contents. But an ECU also has what is called KAM memory (KEEP ALIVE MEMORY), which is neither more nor less than a RAM memory powered directly by the car battery (without going through the ignition key). In a KAM memory, the fault codes that are loaded due to anomalies in the injection system are recorded to ensure that when the car enters the workshop, data is available on which component caused the failure.

The BUS is responsible for transmitting the information. The function that a BUS has within the ECU is to connect one chip to another. In the ECU, instead of using cables as connectors, copper tracks are used as conductors in the printed circuit.


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