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Automotive Computer Reprogramming

 Reprogramming can be done in two methods :

1.Physically in the control unit

2.Through the diagnostic port of the car

Physically in the control unit:

Extracts the memory from the control unit in order to read its original file. This original file is reprogrammed and recorded new in its memory, or in a new one (this depends on the type of memory that the ECU has installed)

Normally the ECU houses the memory inside a socket allowing it to be easily removed.

ECU programming

Basically all these ECUs are identical at the hardware level. They all have a Microprocessor, which accesses the SOFTWARE stored in the memory housed inside the socket.

After accessing the socket that contains the memory chip, we can see that it is made up of two plastics, carefully we can separate them and finally access the memory chip.


When looking at the registered code, we can notice that it is not a commercial code, searching on the Internet we can find more specifications about the chip code.

These memories are similar to the memories used by desktop PCs, they simply contain data cells that are electrically stored and depending on the model, they can be erased for later processing, or in the case of memory with OTP so you are not enabel to programming.

We can also find FLASH memories of this type that are memories identical to the previous ones but they give us the advantage that we can erase them and write to them without the need to have a special lamp to erase them.

What we need is the content of the memory, for this I needed a memory reader that is compatible with said memory. The programmer must bring a CD with software to read the memories. We proceed to read the reader's manual and after understanding how it works, place the memory to be read (Our CHIP) in the appropriate place, configure the program to proceed with the reading.

programmer ecu

Then we will have our reading done and specified in a binary file, If we read a 27c256 we will have a 32kb file and if we read a 27c512 we will have a 64kb file.

What does this file contain?

The binary that is generated after reading the memory is nothing more nor less than the ecu software.

How is this?

As we said before, the main Microprocessor of the ECU does not have a place within them to store Software, so they require an external memory (Our Chip) which contains the Software that It is what will define the behavior of the processor, indicating what and when it has to do the things it has to do.

What are Maps?

As we said, the bin contains the Software. The Software is made up of lines of code that basically acquire information from the sensors (position, rpm, temperature, etc.) to then determine when and how to apply the actuators (injectors, spark, etc.).

This software also has reference tables, which indicate that for a certain input state, it must generate a certain output state. These tables are located in certain positions and are known as MAPS.

How to view the content of the BIN?

quick answer, the bin file contains values that can be seen in Hexadecimal format, for this we use a program that may be similar to WINHEX. This program allows us to open the file and view its content quickly.

dump ecu

And what are all those hieroglyphs?

That is the memory represented in hexadecimal values, these values are interpreted by the ECU microprocessor, which understands and executes what it has to do.

What can I modify?

Generally, what is modified are the parameters located in the tables known as maps, in this way the ecu will generate another output to the same information, allowing us to inject more gasoline or modify the advance or the rpm limiter, or the idle.

Change and just like that?

No. Many ECU memories come with an Integrity Check system, in this case the Corsa's is very simple. This means that if you change a value in memory and do not properly modify the integrity parameter, the ecu DOES NOT START.

What are we going to modify?

The idea is to modify the rpm cutoff by raising it to 6800 rpm, and most importantly recalculate the checksum so that our ECU continues to work. Before continuing, we are going to clarify what the rpm cut is and how to calculate the checksum, and then we continue.

What is rpm cutoff?

rpm = revolutions per minute, that is, the number of turns the crankshaft makes in one minute. The cut is not in rpm values but is modified by a constant. According to the equation below:

Rpm Cutoff = 3,932,490 / (value in address/corresponding position in decimal).

We have already learned how to select a block in WinHex, now we have to go to a memory location.

In this case we are interested in going to position "87D" and "87F".

If we do so we find something similar to this:


As we can see we have at address 87D: 02 5d and at 87F: 02 5c

Note: they are taken in pairs because these particular constants are 16 bits.

Let's proceed to translate this to decimal. 025d Hex = 605 decimal and 025c Hex = 604 decimal.

We had said that the cut was calculated with an equation, so we have to Cut1 = 3,932,490 / 605 = 6,499.98 and Cut2 = 3,932,490 / 604 = 6510.74

Well, we have already determined where the cuts are and what the calculation equation is like.

Cheksum calculation

Now we will explain, as an example, how to calculate the checksum with a commercial program: WINHEX, which can be downloaded in a DEMO version. The first thing we must do is run the program and open our .BIN, in this case the CSUN. Then, as we have said before, the checksum was calculated between memory positions 8 to 32767 or speaking in hexa from 8 to 7FFF.

How do I calculate the checksum?

What we are going to do is "paint" or "select" from 8 to 7FFF with the program, but before doing it with the mouse, we can use a block selection tool, in the "Edit" menu.


We will place in the fields from: 8 to 7FFF.

calculate checksum

The program will automatically select the defined block for us.

automotive repair manuals

And now?

Now, we turn to another WINHEX tool, which will automatically calculate the total sum of the block, and will give us the result.

For that we go to the menu: Tools -> Calculate Hash.

checksum correct

We select the method (Checksum 16) and Accept.


As a result, the Program calculates and we will effectively see that the value obtained is identical to the one located in position 6 and 7.

automotive repair

Is it important to verify this?

Yes very important

This tool, like the soft one that I uploaded in the previous entry, is of utmost importance and necessity, because before recording the memory with the new BIN we must verify that the checksum is correct or else the ECU will not work.

If the checksum is not correct, it can be easily edited with WinHex by putting the value calculated by the tool in positions 6 and 7.

What are we going to modify?

The idea is to modify the rpm cutoff by raising it to 6800 rpm, and most importantly recalculate and repair the checksum so that our ecu continues working.

Where do we start?

To calculate the value of the rpms.

We had said that:

Cut1 = 3,932,490 / (value at address 87D in decimal) and. Cut1 = 3,932,490 / (value at address 87F in decimal)

We are going to leave the two cuts at 6800 rpms, to do this we need to know what value we are going to put in the divider.

We clear

(value at address 87D in decimal) = 3,932,490 / Cut1 and (value at address 87F in decimal) = 3,932,490 / Court2

So (value at address 87D in decimal) = 3,932,490 / 6800. And (value at address 87F in decimal) = 3,932,490 / 6800

following = 578 and = 578

Are these the values that I have to put in memory?

NO. We remember that the memory was in Hexadecimal mode, so we must convert the number 578 Decimal to Hexadecimal, which will give us 02 42.

I already know what I have to put, how do I do it?

Easy, I edit the file locating myself at position 87D and replace the values with the new ones.



NO. The CheckSum needs to be recalculated and corrected.

And how I do it?

Read the previous part carefully which indicates how to perform this checkSum calculation. If we calculate the new checksum value we will obtain as new: 3B F7.

And now?

Now we go to position 6, and we change the value we had for the new value.


Yes, we just need to save the binary with another name so as not to lose the original, and we now have the first modified binary of our ECU.


It wouldn't hurt to double-check the accounts and checksum, just to be sure.

Record the new Bin into a new EPROM memory.

Note: remember that our binary is for a 256 EPROM, if we want it for a 512 EPROM we will have to duplicate the file.

If everything went well, and we verified the values and modifications, we would be able to test the new chip with the correct cut.



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