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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.

 

 



User Feedback

Recommended Comments

Arbe_gtc Rookie

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GM Car Hacking Expert

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On 10/11/2024 at 4:42 PM, Dan79 said:

Whhat option in SPAT do i need to use? its a .bin file and cant find any option to zip that back so its like a original sps cache file

spat, create a new archive. follow the text in the window and make your own files.

Dan79 Top Member

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have a HMI file and what i can see its uses big endian, i get 1288 as checksum on this  file, can anyone confirm that?

I get error when i run the archive in dps 

84229478USA2.5.bin

Arbe_gtc Rookie

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7 minutes ago, Dan79 said:

have a HMI file and what i can see its uses big endian, i get 1288 as checksum on this  file, can anyone confirm that?

I get error when i run the archive in dps 

84229478USA2.5.bin 565 B · 0 downloads

check this

 

 

Dan79 Top Member

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3 minutes ago, Arbe_gtc said:

i have read that several times and followed the directions how to create the checksum  but i dont think im getting it right, can you check if the cheksum i got 1288 is correct for the file ?

 

 

On 10/11/2024 at 4:05 PM, Arbe_gtc said:

use SPAT option in DPS to create the package

 

Arbe_gtc Rookie

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the checksum of this  file es A4 5E, read again my message, HMI uses little

Dan79 Top Member

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5 minutes ago, Arbe_gtc said:

the checksum of this  file es A4 5E, read again my message, HMI uses little

When i try little endian i get 5ea3 then +1    5EA4

Hex value:
5ea3 + 1 = 5EA4

Dan79 Top Member

+Dan79

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1 minute ago, Dan79 said:

When i try little endian i get 5ea3 then +1    5EA4

Hex value:
5ea3 + 1 = 5EA4

Sorry now i can see that it most swap so A4 first then 5E, right?

Arbe_gtc Rookie

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2 minutes ago, Dan79 said:

Sorry now i can see that it most swap so A4 first then 5E, right?

you need swap it, yes

 

Dan79 Top Member

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11 minutes ago, Arbe_gtc said:

you need swap it, yes

 

Thx will test that tomorrow

 

Dan79 Top Member

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Is it possible to get 068B as hex and then with +1 its only 68C  so missing one nummber? or do i use C068?

Arbe_gtc Rookie

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On 8/30/2024 at 10:23 PM, Mindaugas Cernius said:

Hello colleagues. After calculating the CheckSum I got the result f2, how do I write the first four bytes?

 

On 8/31/2024 at 12:26 AM, Robi_X said:

00

@Dan79 same with 3 bytes.

Dan79 Top Member

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so 68C becomes  8C 00  for the hmi file?

Mindaugas Cernius Collaborator

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11 minutes ago, Dan79 said:

so 68C becomes  8C 00  for the hmi file?

123=0123

12=0012

2=0002

 

Dan79 Top Member

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Hi tested this on 2.0 hmi to see if its the same and its very simular  but the 3rd bit is almost always wrong , like on the attached file if i ran the checksum i get 5914  but checksum is 5994   , tried on several files and always the 3rd is off like if oem is 4BE6 I GET 4B06   , do you know why this is , it uses little also

23154070.bin

Arbe_gtc Rookie

+Arbe_gtc

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i dont know what is your problem...

 

image.png.5bd053332d35b7996651b9900e267915.png

Dan79 Top Member

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if you try to calculate thechecksum on this original file you will get 5914  and not 5994 like it should be , try your self and you will see you will get 1458+1=1459  so 5914  and thats wrong , thats why i wonder why 

Arbe_gtc Rookie

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GM Car Hacking Expert

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8 minutes ago, Dan79 said:

if you try to calculate thechecksum on this original file you will get 5914  and not 5994 like it should be , try your self and you will see you will get 1458+1=1459  so 5914  and thats wrong , thats why i wonder why 

i got the correct checksum, you can see it in the previous image

Dan79 Top Member

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please show me the steps as i cant get the correct one at all , im stuiped i know:)

Dan79 Top Member

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the NOT of 6BA7 i get 1458 then +1 =1459      and thats 5914

Arbe_gtc Rookie

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1 hour ago, Dan79 said:

the NOT of 6BA7 i get 1458 then +1 =1459      and thats 5914

I dont know how you get 1458

 

image.png.59e080b8572405a5ccfef76a5954dba9.png

Dan79 Top Member

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  • Contributor

That i understand ,please try this file and tell me what the cheksum is , i have edited  so the first bits are not correct know, i want to check if we get to same conclusion , if i go trough all the steps to check cheksum (little) i get BB2B for this file.

23648990.bin

Arbe_gtc Rookie

+Arbe_gtc

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GM Car Hacking Expert

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17 minutes ago, Dan79 said:

That i understand ,please try this file and tell me what the cheksum is , i have edited  so the first bits are not correct know, i want to check if we get to same conclusion , if i go trough all the steps to check cheksum (little) i get BB2B for this file.

23648990.bin 915 B · 0 downloads

this file its the same

Dan79 Top Member

+Dan79

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  • Contributor

sorry here is it , i get BBAB on this one

23154070.bin

Robi_X Collaborator

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yes i get also BBAB

Arbe_gtc Rookie

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Its BB AB, but if the unedited file ful checksum, is 0x80000 the edited file must be 0x80000.  if you correct checksum and the original file have 0x80000 and the edited file have 0x90000, if i remmember, it fails in programming

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