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ECU: principle of operation, malfunctions and repair


The electronic engine control unit (ECU, ECU or, more precisely, ECM and PCM) is the center that unites the various subsystems of the car. The “viability” of the entire car depends on the correct functioning of this unit: it is he who controls the operation of the engine so that it gives out optimal performance. Therefore, they say that the engine is the heart of the car, and the computer is its brains.

engine control module

The principle of operation of the computer

The control unit is a microcircuit with a microprocessor and software. The task of the ECU is to collect data, process it and issue commands to the actuators.

How it happens:

From the moment the engine is started until it stops, the ECU receives readings from sensors in the engine compartment, exhaust manifold and other subsystems. For example, according to the knock sensor, the ignition timing is adjusted , according to the oxygen sensor, the amount of injected fuel is adjusted, etc.

 The ECU program analyzes the received data according to the performance maps stored in the memory (fuel maps, ignition maps, torque models, etc.) and calculates, for example, how much fuel needs to be injected in a given ICE operation mode.

Then the ECU generates control commands and transmits them to various actuators (injectors, ignition module, fuel pump, XX regulator, exhaust gas recirculation valve, canister purge valve, etc.). In the fuel injection example, the ECU sends an electrical pulse of the desired duration to the injectors.

This whole process takes place in real time and takes into account a large number of variables.

The firmware of modern ECUs can be read, reprogrammed and written back, replacing the standard one. This makes it possible to make significant changes to the operation of the entire car: from disabling certain systems to installing new ones (for example, to install a turbocharger on an atmospheric engine so that the internal combustion engine works correctly).

Malfunctions of the engine ECU

Problems with the block are usually divided into two types:

Regular malfunctions.

Malfunctions of this kind often occur due to shorted wiring and failure of sensors. A defect from the factory can be attributed to the same type of malfunction. For example, in some domestic cars, cases of filling the ECU with antifreeze due to the unsuccessful location of the unit in the car are common. There was such a sore on Kalina that the bad location of the ECU often led to antifreeze getting into it

Malfunctions caused by external interference.

This type includes unsuccessful attempts to flash or repair the ECU. Such malfunctions are much more serious, since problems arise that are unusual for a particular unit. Analysis and troubleshooting can take a long time.

Common Causes of Failure

• Solenoid short circuit;

• Cracks on the board, especially in solder joints;

• Block overheating;

• Corrosion from ingress of moisture or technical fluids, prolonged exposure to humidity, temperature changes (not relevant for all blocks and vehicles).

In general, even a seemingly simple computer repair can lead to big problems for car owners. For example, when replacing an ordinary transistor that has failed, you can accidentally or through inexperience install a transistor of the wrong type, which will lead to overheating of other elements of the board. Usually this entails the failure of the processor and the unit as a whole.

Burnt transistor on the Avtel M73 controller

Also, craftsmen who take up the work of repairing control units and do not have sufficient experience and ability to work with delicate electronics may overheat the elements during the soldering process or install them incorrectly.

Signs of possible problems with the ECU

Weaknesses in the engine block are enough, but it also often happens that the problem is not in the ECU itself. A comprehensive diagnosis of the machine and verification by an experienced auto electrician will help here.

What may indicate a malfunction of the engine block:

• Check Engine caught fire,

• problems with ignition, misfires,

• engine stalls after starting, does not start at all, troit,

• inadequate behavior when pressing the gas pedal,

• arbitrary switching on of the engine cooling system.

More obvious symptoms can be determined by diagnostic equipment: for example, if non-erasable errors have appeared, data from sensors has stopped coming in, or there is no communication with the unit at all.

How to repair an ECU

As indicated above, it is impossible to accurately determine the failure of the unit by the symptoms alone. Therefore, before repair, it is imperative to diagnose the computer, other units, systems and sensors, and check the wiring. When it is precisely established that the reason is in the ECU and it is not of a software nature, the repair is carried out:

Removing the block, dialing the contacts. Opening and external inspection of the board to detect physical faults: breaks, damaged.


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