Electronic Control Unit – The Brain of a Car

If little else, the brain is an educational toy.

–          Tom Robbins


The young man was enjoying the highway in his new car. It was a lovely winter afternoon, traffic was sparse, the asphalt was in pristine condition and his car handled as smooth as silk. Passing another driver, he was surprised to see that the gentleman was disgruntled. “I just cannot get this car to behave properly”, said the other driver, noting the young man’s concerned face. “I wish”, he continued, “that this car had a brain of its own, so it could always give me its best possible performance!” The young man smiled. His new car had something the other didn’t – an electronic control unit.


Ever since the early eighties when computers began to be used in automobiles to meet tight EPA emission control specifications, the idea of fusing computers with automotive engineering has riveted the attention of car manufacturers for years. As the field grew in scope, the quest to stretch automotive technology past its cutting edge has been insatiable. As engine control initially used only a small part of the computer’s actual capacity, engineers soon devised other tasks that could be performed by the computer. Research and innovation have been at full throttle, ultimately attempting to create the seemingly inconceivable – a car with a brain of its own.


They succeeded.


Containing upto a 32-bit, 40 MHz processor, the electronic control unit (abbreviated to ECU) is today capable of turning even the meanest of four-wheeled machines into a pleasurable driving experience. The ECU controls the fuel injection system, ignition timing and the idle speed control system. It also interrupts the operation of the air conditioning and EGR systems, and controls power to the fuel pump (through the control relay). The ECU consists of a microprocessor, random access memory (RAM), read only memory (ROM) and an input/output interface.


Typically located behind the glove compartment, underneath the dashboard, the ECU operates based on data from the input sensors (engine coolant temperature, barometric pressure, air flow etc.), used to interpret the vehicle’s needs. The electronic control unit makes continual adjustments to the engine’s fuel delivery circuits as well as the ignition timing. These tweaks help provide the proper air-fuel mixture being ignited at the optimal time in the combustion chamber. This ensures the vehicle is operating at the utmost peak power and economy level.


Impressive as it seems already, there’s more. Those on-the-fly adjustments are not limited to the car’s engine. The transmission’s torque converter, in cars with automatic transmission, is locked and unlocked according to information received by the ECU. By locking the torque converter the ECU is able to eliminate transmission slippage, and thus preventing wastage of precious fuel. The optimal shift points for the transmission are also determined by the ECU based on feedback from the engine, which takes advantage of the peak horsepower and torque produced.

As if all these weren’t enough of a chore for the ECU, the little guy also monitors oil condition and maintenance schedules. By means of sensors within the engine the unit is able to decipher the proper intervals for scheduled maintenance. If a problem within the drivetrain is detected, the ECU sends a message to the driver via a message board on the instrument cluster. And if a fault is found in any part of the vehicle’s electronics system, the ECU flashes a code directing service attention to the correct area.  In the cold climates, the electronic control unit ensures proper application of fuel to provide a smooth cold weather start.


Often making adjustments thousands of times per minute, the electronic control unit is akin to having practically a super-skilled mechanic to continuously monitor and improve the car’s performance. Eradicating the worries from the driver’s head altogether allows him to take in, wholeheartedly, the uncompromising thrill – and joy – of driving a car. Whether it’s the lazy Sunday morning drive or the exhilarating screech of burning rubber on a racetrack, the electronic control unit ensures that the driver’s pulse beats in tune with the vehicle’s – all the while coming one step closer to creating the ultimate fusion –  of man and machine.






(-by Abhishek Neeli)



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