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What is an Electronic Control Unit?

By Lori Kilchermann
Updated May 17, 2024
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The electronic control unit (ECU) is the brain of the automobile. This small device is typically located behind the glove compartment, underneath the vehicle's dashboard. Modern automobile design uses many electric components that determine fuel delivery, transmission shift points and ignition timing, to name only a few. These components take direction from the ECU, which controls all electronic functions within the vehicle's drive train.

Actually a small computer, this unit takes readings from all of the vehicle's electronic sensors and interprets the vehicle's needs. In order to operate at the peak fuel mileage and performance, it makes continual adjustments to the engine's fuel delivery circuits, as well as the ignition timing, to provide the proper air and fuel mixture being ignited at the optimal time in the combustion chamber. This helps ensure that the vehicle is operating at its peak power and economy level possible.

Important on-the-fly adjustments are not limited to the vehicle's engine by the electronic control unit. The transmission's torque converter, in an automatic transmission-equipped vehicle, is locked and unlocked according to information received by the device. By locking the torque converter, the ECU is able to eliminate fuel-wasting transmission slippage, which equates to higher fuel costs for the owner. The unit also determines the optimal shift points for the transmission based on feedback received from the engine, which takes advantage of the peak horsepower and torque produced.

Many of the vehicle's components and engine systems can be monitored by the control unit, including the oil condition and maintenance schedules. By taking readings from sensors within the engine, the ECU is able to decipher the proper intervals for scheduled maintenance. When a problem within the drive train is detected, the device sends a message to the operator via a message board in the instrument cluster.

The electronic control unit adjusts how fuel is used in cold climates to ensure a smooth start and trouble-free operation in any weather. Often, making adjustments many thousands of times per minute, the unit is like having a personal mechanic riding along to keep things running smoothly. When there is a problem with any part in the vehicle's electronic system, the device is able to flash a code directing the service attention to the correct area.

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Discussion Comments
By mopwise — On Jul 01, 2012

What is the function of an electronically controlled transmission system?

By Charred — On Aug 29, 2011

@hamje32 - I had a bad car control unit once. Like you said, it can be hard to figure out where the problem is.

My car would be driving okay, and then all of the sudden I would get a sudden injection of fuel at the wrong times; it seemed as if the car wasn’t getting the right ratio of fuel to air mixture.

Naturally, I assumed that the fuel pump was at fault. I replaced that unit, and still the problem remained. It was only after taking it to the mechanic – and paying a lot of money – that I was told the problem was the car control unit.

It’s involved in managing fuel delivery, among other things, just like the article says. So the ECU wasn’t making the proper adjustments and I was getting sudden injections of fuel at the wrong time.

Cars nowadays are so computerized that only a car shop with computer systems could figure this stuff out.

By hamje32 — On Aug 28, 2011

I had a 94 Honda Civic with about 150,000 miles on it, and one day it just died. It wouldn’t start at all. At first I thought it was the alternator or something like that, but these were fine.

I had friend who was a mechanic come and look at it. Through some tinkering, he told me the computer was bad. It was totally shot.

The thing you have to realize is that you can’t just go to an automotive store and pick up a new computer, or engine control unit as it is called. You have to order it because it is custom made for the make and model of your car.

Fortunately, my friend offered to look at the local auto scrap yard. He found the right computer for my car and now it works fine. I don’t know how much I would have paid had I ordered it brand new.

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