PrimeChecksum · Checksum correction
ECU Checksum Correction: What PrimeChecksum Does and When You Need an External Tool
An ECU checks the integrity of its software with a checksum: if the data in the file changes and the checksum is not updated, the ECU may reject the file and the vehicle may not run. In EcuPrime, checksum correction lives in its own tab (PrimeChecksum) and is not added automatically to a coding delivery. This page explains what the tab does, when a correction is made and when you need an external tool.
PrimeChecksum
What does the Checksum tab do?
Identifies the ECU from the file
Even if you do not enter the make or the ECU, the system identifies the ECU from the file you upload.
Asks for the original if needed
On some ECUs the comparison needs the original (factory, unmodified) version of your modified file; the system asks you for it. The original must be the same size as the modified file.
Only your own file
The output is the file you uploaded with its checksum corrected; the changes in your file are kept.
Credit only on a result
Checksum correction happens inside the platform, in a separate tab: 1 credit, charged only when the result is ready. Some newer-generation ECUs (RSA-signed) need an external tool; the system detects this and warns you.
Cases
When is it corrected, and when do you need an external tool?
A recognised, supported ECU
When the system recognises the ECU and can correct its checksum, it prepares the result; credit is charged only when the result is ready.
Modern signed ECU (RSA)
On modern signed ECUs (for example the MED17 / EDC17 / MG1 class) the checksum is not corrected by the system; an external tool or your own device is needed instead. The system detects the families it knows and warns you.
Unrecognised ECU
On an unrecognised ECU no checksum is written: no blind correction is made.
A file that was not changed
If PrimeChecksum made no change to the file, it says so clearly and no credit is charged for that result; the checksum is not thereby independently verified as correct. Check it with another tool before writing.
Before writing
Why is it needed before writing?
The ECU checks the checksum
When the data in the file changes, the checksum has to be updated too; an ECU may reject a file written with a checksum that was not updated, and the vehicle may not run.
Not done automatically on delivery
The checksum is not corrected automatically in the file the software delivers; the notice is explicit: “Checksum correction is recommended.” Use the Checksum tab or your own tool.
The result is a file calculation
The checksum result is a calculation on the file; it does not mean the file will work in the vehicle's ECU. Back up your ECU before writing; verifying the checksum state is the user's responsibility.
Got an Autotuner, Flex, KESS3 or Dimsport file?
How the file you read with your tool is uploaded to the software: which file, which formats, full and partial reads, encrypted slave packages and the checksum before writing.
Want to edit the file yourself?
EcuPrime Studio runs in the browser: edit maps in Hex, Table, 2D and 3D view, list ORI/MOD differences and save versions.
Help
Frequently asked questions
What is a checksum, and why is it corrected?
A checksum is the control value an ECU uses to check the integrity of its software. When the data in the file changes, this value has to be updated too; if it is not, the ECU may reject the file and the vehicle may not run.
Is the checksum done automatically?
The checksum is not corrected automatically in the delivered file. Checksum correction happens inside the platform, in a separate tab: 1 credit, charged only when the result is ready. Some newer-generation ECUs (RSA-signed) need an external tool; the system detects this and warns you.
Which ECUs need an external tool?
On modern signed ECUs (for example the MED17 / EDC17 / MG1 class) the checksum is not corrected by the system; an external tool or your own device is needed instead. The system detects the families it knows and warns you.
Is a checksum written if my file is not recognised?
No. On an unrecognised ECU no checksum is written: no blind correction is made. In that case you need to verify the checksum with your own tool.
Why am I asked for the original file?
On some ECUs the checksum comparison needs the original (factory, unmodified) version of your modified file. The original must be the same size as the modified file; credit is charged only when the result is ready.
How many credits does checksum correction cost?
A checksum job costs 1 credit, charged only when the result is ready. If PrimeChecksum made no change to the file, no credit is charged.
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