ECUs Explained

ECU stands for Electronic Control Unit. In modern motor vehicles it is used to control various elements of operation, particularly regarding engine control. Put another way it is a computer that aids in driving/controlling your vehicle. ECUs have been around for quite a number of years in motor vehicles but have become more and more sophisticated and whereas before they would only be found in top end sport/luxury vehicles they are now pretty much standard in every vehicle that comes off the production line. 

ECUs in motor vehicles really started out with fuel injection engines to monitor and control all elements of the injection system, from fuel used to air temperature and flow. Today they will incorporate the security system, lighting, brakes, mileage odometer etc. 

A vehicle can have more than one ECU, you may find a separate ECU for the injection system and another for the braking system etc. 

What are the benefits of ECUs? 

Like with any piece of engineering, computer control makes running more efficient, more controllable and saves the user having to make manual changes. Years ago you’d be sitting turning a screw with a screwdriver on your carburetor to control the fuel used to tune the engine. Starting a cold engine meant pulling a choke out manually to compensate or at best you had a heated element to do it for you. Today the computer can monitor the air, the exhaust gases, the precise temperatures and vary the fuel precisely without you lifting a finger. All you need do is turn the key (or even press a button!). 

While many people may think maintaining cars has become more difficult with the introduction of ECUs they do actually make fault diagnosis much easier for the modern mechanic. The ECU will not only monitor certain parts of the vehicle for its own data requirements but also report them as faulty if they do not respond as expected. The faults are stored in the ECU for a mechanic to retrieve later on. On top of that if a certain part should fail during operation the ECU will alter other settings to keep the vehicle running, if possible – this is referred to as Limp Home Mode. To do this it normally feeds in assumed settings for the faulty part. 

OBD? 

The feature of storing and retrieving faults and other data is called On Board Diagnostics (OBD) – explained here . Reading the information can be done in several ways. The most basic system is to read fault codes denoted by a flashing LED or the Diagnostic light on the dashboard. Simply, it will flash once to denote 1 and flash twice to denote 2 and so on. These fault codes are then indexed with the given faults from the manufacturers listing. For instance fault code 14 may refer to the ‘coolant temperature sensor’. Generally, your next course of action would be to further test or replace that component. 

ECU Mapping 

The ECU like all computers is controlled by a set of instructions to operate from. These instructions are referred to as the MAP or software in it. An ECU maybe re-mapped as the manufacturer has updated settings to iron out previous bugs or by individual tuners who want to alter the performance of a vehicle. 

On early ECUs, re-mapping was only possible by physically removing the complete ECU or a chip from within it and reprogramming it. On some later OBD-II compatible models this is possible simply via the OBD port in the vehicle.

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