I'm new to the ECU (or chip) tune concept, and I try to understand what is going on there.

I understand the concept and the goal, but I'm having difficulties to understand what is actually going on there.

From what I understand the process for tuning is:

  • Download ECU firmware from the car.
  • Modify some constant values (in the map).
  • Write the modified ECU back to the car.

However, I can't understand what is the format of the downloaded ECU - is it just a regular firmware? I found many websites like this which offer to download ECU files, but I couldn't recognize the format - it doesn't look to me like any firmware, and I couldn't identify any CPU architecture on all the files I tried. In addition, the size of the files is almost always 512KB, 1024KB or 2048KB which is not very typical to firmware.

When downloading files from those sites I see that many of them referenced as ori (original?), some of them as map and some of them as bdm. (Needless to say, there is not much information about the formats in the sites..). What do these types mean?

  • Not sure I have found a file format called "firmware"... csv, txt, and many others
    – Solar Mike
    Commented Jul 29, 2019 at 9:13

2 Answers 2


The file format is just hexadecimal, it isn't human readable it's just hex stored usually as a .bin file however some tools and software have their own extension such as .cod .dtf etc. The file extension doesn't matter as the content is the same.

The reason the file size is 512KB, 1024KB or 2048KB or in multiples of is because these are common sizes of flash storage used to save the map contents in the ECU and when you download the firmware the tool will give you the complete contents including blank space.

The 'maps' can be stored in the microcontroller or in a separate flash or Eprom chip on the PCB.

BDM is just a format for reading the ECU contents through a dedicated connection directly on the PCB, this is getting more and more redundant as modern tools are getting better at downloading through the OBD port.

You can read the files with just normal hex (hexadecimal) editors. When a tuner is modifying the contents they just search the hex for known patterns that are lookup tables. There are thousands of lookup tables such as throttle position vs rpm, coolant temp vs rpm etc etc. Typically for a stage one map you would change between 80-120.

Using a standard hex editor to tune a file is possible but very labour intensive, so there is plenty of software that plots the hex value on a graph against its location to give you a 'image' of the data, something the human eye can recognise quickly and easily. The software also lets you save each look up table (map) so you can open it as a table and change the values in each column or row.

To get a feel for what you are dealing with you should download a free hex editor and open the file, see if you can find rows and columns of the lookup tables. RPM values are easy to find as they are typically in multiples of 250. When you know how the data works you will get a better understanding of what the tuning software is doing and how to use it.

  • If you found this answer useful please upvote as well as picking best answer, thanks! Commented Aug 4, 2019 at 11:44

Most manufacturers have that their own proprietary systems. Search for manufacturers Techservice website or Techinfo. Toyota calls it TIS. Nissan is NTI for examples. The ability to accurately read this information can be tricky. It usually requires use of a license or subscription.

When attempting to access these files from my particular vehicle I found the cars log files were encrypted. Attempting to read them may be possible but not without additional software. Hence the tuner software you buy. To actually change values, 1s or 0s or any decimal could be ill advised. The CAN network for the module you're recoding be become incommunicable or unable to communicate. This may require you to find other means of reinitializing the module.

If your ECU "tuner" utilizes functions from the manufacturer it's a high chance they bought a subscription just like you could. I've seen rental fees for it's use per day with a state license required . Various organizations meeting "standardized" criteria for providing said licenses lol.ASME is a decent place to start.

Automotive vehicles architecture is the CAN bus- both high and low speed. Through the use of electronic controllers. See PLC or DDC controls.

A good resource is Forescan for Mazda/Ford. As built data. These manufacturers used to use PATs, IDS, MDS and Nissan had Consult 1 through 3 . Those are manufacturers bread and butter for making money. The files are usually encrypted. Of course for X fee, they'll sell you the same key your ECU programmer should be using. Cobb Tuning for reference

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