What is ECU remapping?

So what is all the fuss about?

Here we will answer the question ‘What is ECU Remapping’ in a way that is understandable without all the ‘smoke and mirrors!


To begin it will help to understand what an ECU is, then we will move forward to explore the remaining component of our question, what is remapping, or specifically ECU remapping.

What is an ECU:

The term ECU is an acronym for the phrase ‘Electronic Control Unit’ and not as many believe ‘Engine Control Unit’. Let me qualify this for you. Most modern vehicles are fitted¬† with several ECU’s, some will control safety devices, some traction control and drive systems and yes at least one will control engine functionality. The correct term for this last ECU is the ‘Engine ECU‘ which is the one that we are interested in.

How Does an Engine ECU Work?

So now that we know what an ECU is and that the ECU relevant to our question is an Engine ECU, How does it work?

The fundamentals of control engineering stipulate that to control something you must first be able to monitor its function, then have a means to alter its behaviour that will in turn change the function that you are monitoring.

If we now look at our Engine’s Electronic Control Unit (ECU) we can say that it monitors the functionality of the engine by way of various sensors that feed their information back to the ECU and based on these inputs the ECU then changes engine functionality that is under its control until the inputs from the sensors on the engine provide feedback that meets a set of pre defined values.

Most if not all engine ECU’s are simply small computers with 4 or possibly 8 bit processors, of which some have external read only memory (ROM) where the control ‘software’ is stored, others have this ROM built into the processor ( The Chip ). There will also be some EEPROM or FLASH type memory where data can be read and wrote to. EEPROM / FLASH type memory is similar to that used in USB sticks and is memory that retains its data when power is removed.There will be some I/O interface electronics ** (see note below), basically the bits that allow the processor to get data from engine sensors and to control some engine functions. That is the technical bit done with!

** Modern vehicles use what is called a CAN network to relay data around the vehicle, allowing various ECU’s to communicate with each other. The CAN interface is serial interface that allows for it deployment over single or twin wire networks.

We now have enough information to provide a simple working concept for our engine’s ECU.

When ignition voltage is supplied the processor in our engine ECU will ‘Boot up’ / initialise itself and run its software. This software will monitor the data provided via its I/O electronics and compare these data values against a set of pre defined values. If the values it is receiving compare favourably with its pre set data values it does nothing. If however one of these values is too low, too high or outside a range of values that it has in its pre set data, then it will send an output that will change some part of the engines function until the values it is reading are acceptable.

Here are just ‘some’ of the engine functions that the engine ECU monitor and control are:

  • Air / Fuel Ratio
  • Ignition Timing
  • Idle Speed
  • Variable Valve Timing (VVT)
  • Electronic valve control.
  • Engine rev limit

The bit you have all been waiting for!

In the previous section take note of the phrases ‘pre defined values’ and ‘pre set values’, I have highlighted them both. These values are what we call a ‘look-up table’. This look-up table is where the software that is running on our engine’s ECU looks up the value that it will compare with the value that it is receiving from a specific sensor on our engine. The values in the look-up table can be maximum values, minimum values or a range set by a minimum and a maximum. These are the values that the software running on our engine ECU will use when it is deciding what output signals to send to the engine to change how our engine functions / performs. These values in the ‘look-up’ table are also known as ‘The MAP‘ and so to REMAP the engine ECU is to change the values in this look-up table.

You should now understand what ECU Remapping is, it is the process of changing values in a data look-up table that is used by an engines electronic control unit to decide what, when and how to change engine functionality that is under its control.


The control of a vehicle’s engine via an ECU is said to be done in ‘real time‘, or continuously while the engine running or has ignition voltage supplied to it. So remapping an engines ECU could be called ‘real time functional tuning‘ or ‘dynamic tuning‘ as opposed to more traditional ‘fixed‘ engine tuning such as cylinder head skimming, valve seat polishing and carburettor fuel mixture ratio settings which once changed remain constant during engine operation..

Why Remap an Engine’s ECU?

The sceptics amongst you will probably be asking

‘ If you can give me all of this extra engine power, improved MPG and extra torque by remapping my engine’s ECU, then why do the manufacturers not do this? ‘.

Here is your answer:

Vehicle manufacturing was probably one of the first industries in the world to adopt ‘globalization’. Having a small number of manufacturing bases that supplied various global markets. Each of these markets being identified by common sales and production cost factors and not geographic factors, although there is often a correlation between the two. A prime example is the European market or ‘selling into Europe’. Given that certain regulations relating to engine performance / emission control and the like are controlled by a central regulatory body, it is easy to see why vehicle manufacturers would produce a vehicle with an engine performance profile that meets all EU regulations, but also meets all local EU country profiles in terms of emission control, service availability, fuel & road qualities. This then allows them to reduce production costs, which will equate to more profits.

When you look at the manufacturers literature for many of what we think of as ‘performance cars’, BMW, Mercedes, Audi etc the standard 4 door versions are promoted as either ‘family saloons’ or ‘ideal economical fleet cars’, not as ‘ideal traffic light racers’ or ‘can normally be seen hugging the outside lane of motorways’, cars!. This applies to all manufacturers of domestic vehicles, and the performance profiles of their engine’s are set to match.

So taking the global market, sales and profit benefits of standardising the tuning of an engine for a target ‘sales market’ and the profiling of the engine for the sales sector the vehicle is intended for, you end up with an engine that is tuned to give maximum profit to the manufacturer.

Living in the UK there are many factors within the tuning of your engine that are not relevant, we have better than average EU fuel quality, better than average EU road quality and better than average EU service availability, to name but a few. So if you are driving a vehicle that was manufactured for the European market, which the UK is a part. Then your engine ‘probably’ is not performing at its peak efficiency in terms of power, torque or fuel economy.

By remapping your engine’s ECU we can adjust the tuning to match conditions here in the UK while at the same time bias any changes to, maximize acceleration & speed, improved torque (pulling power), improved MPG or any variation between these maximums to suite your own personal requirements.