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Troy

By Troy

How to correct checksum after editing GM's calibration files

Update 2/October/2025

You no longer need to manually correct the checksum of the GM calibration files. You can automatically correct the checksum of modified GM calibration files online using this checksum tool, which was created by a CameraLoops member.

The online checksum tool can be accessed from the website's top menu, under the "Tools & Games" button, or via the following web link. GM Online Checksum Calculator

Massive thanks to ECU-Online.com

Screenshot 2025-10-02 at 7.33.39 am.jpg

In this tutorial, I will explain in steps how to correct the checksum after editing a GM module calibration file.

This process illustrates correcting the checksum for the first four bytes.

 

It's beneficial to read up on these other tutorials to familiarise yourself with GM's calibration files concept if you're new. 

 

 

Tools you will need.

 Hex Editor Neo

 

 

Step 1.

Open the calibration file in Neo and edit your file.

Set Predefined Layouts as Expert User Layout.

Screenshot 2021-08-01 at 11.43.56 am copy.png

 

Step 2.

Select all the codes in the calibration file except the first four bytes/code.

How to correct checksum after editing GM's calibration files

 

Step 3.

At the bottom of Neo click Checksum.

Screenshot 2021-08-01 at 3.33.41 pm copy.png

 

Step 4.

In Neo's checksum window, change the option: Whole document to Selection only.

Screenshot 2021-08-01 at 3.40.24 pm copy.png

 

Step 5.

Select Sum of Big-Endian 16-bit value 

Screenshot 2021-08-01 at 6.56.16 pm copy.png

 

Step 6.

Click the  Refresh button.

Screenshot 2021-08-01 at 7.01.14 pm copy.png

 

Step 7.

Copy the last 4 digits, which is: 9730 

Screenshot 2021-08-01 at 7.01.14 pm copy.png

 

Step 8.

Convert 9730 into Binary code, then copy paste the binary code in a text editor.

Screenshot 2021-08-01 at 7.14.03 pm copy.png

 

Step 9.

Now you need to create a reverse copy of the binary code: 1001011100110000, see the example below.

Screenshot 2021-08-01 at 7.23.31 pm.png

 

Step 10.

Convert the reverse binary code 0110100011001111 into hexadecimal code, which equals to 68cf 

Screenshot 2021-08-02 at 12.03.51 am copy.png

 

Step 11.

Now you need to add 1 to the hexadecimal code, which looks like this 68cf+1=

Use this online calculator to do the calculation.

68cf+1=68d0

Screenshot 2021-08-02 at 12.25.20 am copy.png

 

Step 12.

Now you have 68d0

Replace the first four unselected bytes/code in the calibration file with 68d0.

Screenshot 2021-08-02 at 12.34.20 am copy.png

 

Step 13.

The checksum has been corrected.

Save the calibration file and program your calibration package to the module using GM DPS.

 

 



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    stachu22 Explorer

    +stachu22

    +Purchaser

    I tested it and not working for me. I have the same calib file like you, change the same byte  (09 from a5 to a4) and write the same checksum to file - dps stop at 0% with error 😞

  • Quote
    • MNP Apprentice

    MNP

    Member

    The way I find the easiest is to set the first two bytes in the file to FF FF, calculate the big-endian 16-bit, take the last 4, i.e. 2F B5, use the Hex Calculator to do FFFF - 2FB5, giving us a result of D0 4A. Fill the first two byte with that checksum and bam, it's correct.

    icon-16x16.png Hex Calculator

    WWW.CALCULATOR.NET
    This free hex calculator can add, subtract, multiply, and divide hexadecimal values, as well as convert between hexadecimal and decimal values.

     

  • Quote
    • Like 1
    • Thanks 2
    nev3r Enthusiast

    +nev3r

    +Contributor
    • Contributor
    On 6/2/2022 at 12:26 AM, MNP said:

    The way I find the easiest is to set the first two bytes in the file to FF FF, calculate the big-endian 16-bit, take the last 4, i.e. 2F B5, use the Hex Calculator to do FFFF - 2FB5, giving us a result of D0 4A. Fill the first two byte with that checksum and bam, it's correct.

    icon-16x16.png Hex Calculator

    WWW.CALCULATOR.NET
    This free hex calculator can add, subtract, multiply, and divide hexadecimal values, as well as convert between hexadecimal and decimal values.

     

    After trying guide by Troy i just stubbled upon this comment - as yes its way easier doing the way you wrote ! Thanks

  • Quote
    • Like 1
    Selfish mr fixing Top Member

    Banned-Selfish mr fixing

    Banned-Banned

    good day to you troy.

    what type of software you are using to modify the calibration files?

  • Quote
    • Troy Grand Master

    Troy

    Administrator

    GM Car Hacking Expert

    3 hours ago, mr fixing said:

    good day to you troy.

    what type of software you are using to modify the calibration files?

     

    A hex editor 

     

  • Quote
    • Arbe_gtc Rookie

    +Arbe_gtc

    +Contributor

    GM Car Hacking Expert

    • Contributor

    im getting error using the same file as @Troy 23402917 changin the same byte... in DPS any idea? 23402917CORR

    ProgramLog_hmi.Txt

  • Quote
    • Abdulazizxoja Rising Star

    Abdulazizxoja

    Member

    Спасибо Трой 

  • Quote
    • Arbe_gtc Rookie

    +Arbe_gtc

    +Contributor

    GM Car Hacking Expert

    • Contributor
    22 hours ago, _mrv_ said:

    If it is not too late, try this one

    23402917CORR_CS.bin 441 B · 3 downloads

    I already resolved it. some calibrations are calculated in little-endian, and others in bigg-endian (the HMI uses little)

     

    thanks!!

  • Quote
    • Like 1
    PLSA Top Member

    +PLSA

    +Contributor
    • Contributor

    How to apply this to Global Can B?

  • Quote
    • Vauxhall_Mark Collaborator

    Vauxhall_Mark

    Member
    On 3/16/2023 at 12:22 PM, Arbe_gtc said:

    I already resolved it. some calibrations are calculated in little-endian, and others in bigg-endian (the HMI uses little)

     

    thanks!!

    Care to share exactly what you did? I'm going to try and write an app to automate it.

  • Quote
    • Arbe_gtc Rookie

    +Arbe_gtc

    +Contributor

    GM Car Hacking Expert

    • Contributor
    1 hour ago, Vauxhall_Mark said:

    Care to share exactly what you did? I'm going to try and write an app to automate it.

    Open somes calibrations file of different units (BCM, IPC, HMI...) with hex editor neo. And use the checksum option, select "all document" to check the checksum of all the file and calculate Little-endian 16 and Big-endian 16. then you have results. (i dont know if there are more ecus with oter type of checksum. probably no)

    If you look the result of the checksum, you can see 0000 or FFFF in 16 big, or 16 little. Only in one of them. then with this you can know if is little 16 or big 16.

    You careful with this: If the result of checksum is FFFF you  dont need add nothing to correct checksum. if the result is 0000, you need add +1 to the result and in some cases, the result of the checksum must swap (i see this in K74 HMI and K26 AFL module K26 in astra K uses both types of checksum big-end 16 in some files, and little-end 16 in other.)

    I cant tried all units, but check the type of checksum uses is easy.

    the method for calculate the correction, we know it 😛

  • Quote
    • Like 1
    • Thanks 1
    Vauxhall_Mark Collaborator

    Vauxhall_Mark

    Member
    1 hour ago, Arbe_gtc said:

    Open somes calibrations file of different units (BCM, IPC, HMI...) with hex editor neo. And use the checksum option, select "all document" to check the checksum of all the file and calculate Little-endian 16 and Big-endian 16. then you have results. (i dont know if there are more ecus with oter type of checksum. probably no)

    If you look the result of the checksum, you can see 0000 or FFFF in 16 big, or 16 little. Only in one of them. then with this you can know if is little 16 or big 16.

    You careful with this: If the result of checksum is FFFF you  dont need add nothing to correct checksum. if the result is 0000, you need add +1 to the result and in some cases, the result of the checksum must swap (i see this in K74 HMI and K26 AFL module K26 in astra K uses both types of checksum big-end 16 in some files, and little-end 16 in other.)

    I cant tried all units, but check the type of checksum uses is easy.

    the method for calculate the correction, we know it 😛

    My basic excel macro calculates checksum from the endian result, that's first stage but saves a little time. 

  • Quote
    • Like 1
    Vauxhall_Mark Collaborator

    Vauxhall_Mark

    Member
    On 10/20/2023 at 6:05 PM, Arbe_gtc said:

    Open somes calibrations file of different units (BCM, IPC, HMI...) with hex editor neo. And use the checksum option, select "all document" to check the checksum of all the file and calculate Little-endian 16 and Big-endian 16. then you have results. (i dont know if there are more ecus with oter type of checksum. probably no)

    If you look the result of the checksum, you can see 0000 or FFFF in 16 big, or 16 little. Only in one of them. then with this you can know if is little 16 or big 16.

    You careful with this: If the result of checksum is FFFF you  dont need add nothing to correct checksum. if the result is 0000, you need add +1 to the result and in some cases, the result of the checksum must swap (i see this in K74 HMI and K26 AFL module K26 in astra K uses both types of checksum big-end 16 in some files, and little-end 16 in other.)

    I cant tried all units, but check the type of checksum uses is easy.

    the method for calculate the correction, we know it 😛

    Got it basically working can edit any value and re-checksum.  Been testing with my HMI, enabled a few options to test Climate App, Touchpad, front camera etc. @codebuilder not as polished as yours but only a proof of concept, I'll code it up properly in visual studio when I get a chance. 

    20231021_165807.jpg

  • Quote
    • codebuilder Community Regular

    +codebuilder

    +Contributor

    GM Car Hacking Expert

    • Contributor
    3 minutes ago, Vauxhall_Mark said:

    Got it basically working can edit any value and re-checksum.  Been testing with my HMI, enabled a few options to test Climate App, Touchpad, front camera etc. @codebuilder not as polished as yours but only a proof of concept, I'll code it up properly in visual studio when I get a chance. 

    20231021_165807.jpg

    Hey, it does the job!!! haha, nice work :).  At least you've made a quick way to do it.

  • Quote
    • KiT71 Enthusiast

    +KiT71

    +Contributor
    • Contributor
    On 22.10.2023 at 00:08, codebuilder said:

    Эй, это делает свою работу!!! хаха, хорошая работа :). По крайней мере, вы нашли быстрый способ сделать это.

    Hello, can you give me your WhatsApp or write to me?

  • Quote
    • Vauxhall_Mark Collaborator

    Vauxhall_Mark

    Member
    10 minutes ago, KiT71 said:

    Hello, can you give me your WhatsApp or write to me?

    Regarding? 

  • Quote
    • KiT71 Enthusiast

    +KiT71

    +Contributor
    • Contributor
    3 minutes ago, Vauxhall_Mark said:

    Касательно? 

    I want to buy a program for recalculating checksums

  • Quote
    • Vauxhall_Mark Collaborator

    Vauxhall_Mark

    Member
    2 minutes ago, KiT71 said:

    I want to buy a program for recalculating checksums

    It's not really something that's ready, it basically works but just something I knocked up in a couple hours. Currently only testing on HMI files but managed to get all the options I wanted working. 

     

    I can enable something on an HMI file for you if that helps? 

  • Quote
    • codebuilder Community Regular

    +codebuilder

    +Contributor

    GM Car Hacking Expert

    • Contributor
    6 hours ago, KiT71 said:

    I want to buy a program for recalculating checksums

    Are you hoping to modify lots of calibrations?  Not all types of modules work the same for checksums.  I've already had to figure out quite a few.

  • Quote
    • Vauxhall_Mark Collaborator

    Vauxhall_Mark

    Member
    3 minutes ago, codebuilder said:

    Are you hoping to modify lots of calibrations?  Not all types of modules work the same for checksums.  I've already had to figure out quite a few.

    More of a proof I can do it really, I've added menus/code to calculate little and big endian. 

     

    What other methods are you aware of? 

  • Quote
    • KiT71 Enthusiast

    +KiT71

    +Contributor
    • Contributor
    6 minutes ago, codebuilder said:

    Вы надеетесь изменить множество калибровок? Не все типы модулей одинаково работают с контрольными суммами. Мне уже пришлось разобраться со многими.

    Yes, I would like to buy something to change the calibrations in the dashboard and more often in the comfort unit, can you give me your WhatsApp and discuss everything there?

  • Quote
    • Rustam Abdullayev Apprentice

    Rustam Abdullayev

    Member

    Hello Troy,

    Hope you are doing well.

    I am going to calculate the checksum of the GM BCM EPROM, I have followed the instructions outlined in this article but to no avail. Please help me to calculate the checksum of EPROM is the same steps or not. 

    for more information, I have not edited the EPROM and calculated the checksum to compare the original result but result of checksum is different.

    toza eprom bcm.bin

  • Quote
    • Arbe_gtc Rookie

    +Arbe_gtc

    +Contributor

    GM Car Hacking Expert

    • Contributor
    9 minutes ago, Rustam Abdullayev said:

    Hello Troy,

    Hope you are doing well.

    I am going to calculate the checksum of the GM BCM EPROM, I have followed the instructions outlined in this article but to no avail. Please help me to calculate the checksum of EPROM is the same steps or not. 

    for more information, I have not edited the EPROM and calculated the checksum to compare the original result but result of checksum is different.

    toza eprom bcm.bin 4 kB · 0 downloads

    the chekcsum corrections applies to modules calibrations, no to the BCM (or other units) eeprom

  • Quote
    • Like 1
    Rustam Abdullayev Apprentice

    Rustam Abdullayev

    Member

    @Arbe_gtcThank you for the fast answer. Does it mean eprom no need for a checksum?

    But when I tried to edit EPROM the check it in DPS to get info I got the result that EPROM fault. 

    EPROM FAULT.png

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