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Author Topic: Understanding Checksums  (Read 11402 times)
Low01Turbo
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« on: June 28, 2011, 06:05:38 PM »

First, I'd like to say hello, my name is Chris, and I'm car crazy.  I've been around cars for quite some time, and I have an affinity for VAG & Porsche products.  I just wanted to congratulate Tony and the rest of the community for the awesome wealth of information you've made available here.

I've been lurking for some time, but I finally decided to join and start playing.  I'm not a programmer, nor do I understand C++ or HEX, but I do understand tuning and EFI systems.  Nefmoto's software will hopefully help me achieve my goal of a home-brewed, home-tuned turbo setup in my Audi.

SO... my questions...

I'm having trouble wrapping my head around checksums.  I understand they are a type of security and I understand that incorrect checksums can lockout the ECU (or worse), but I don't understand how they must be corrected.

Are checksums unique to each individual ECU? Or do, for instance, two similarly equipped cars from the same year and the same VIN run have the same checksums in their ECUs?  Using Tunerpro, what modifications to the maps will actually change the checksums?  And if they are changed, how will I know they don't match before reflashing the ECU?

I've seen a few products that will check and fix checksums for you, but before I invest in,  say ECUfix, I want to understand the checksum issues and learn what I can and cannot do without fixing checksums.

Thanks for any help in advance.

-Chris
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Matt Danger
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« Reply #1 on: June 28, 2011, 07:35:09 PM »

Checksums exist to verify the integrity of data and ensure the data has not changed. Your car's engine management system uses checksums to protect the engine components in the event the data on the ECU were to be corrupted or changed accidentally.

Checksums are embedded in the ECU file. The same model ECU will have the same checksum values, because the code on the ECU is the same. They are calculated using data in the file. The ECU contains a few different checksums, depending on the ECU model.

The ECU will recalculate some checksums every startup and compare the values to the one stored in the ECU. If they do not match the stored checksums it assumes data has been corrupted and will not allow the engine to start to prevent possible damage or other annoying things.

When you modify the ECU file you absolutely should recalculate the checksum values. This would be tedious if done by hand but fortunately for us MTX-Electronics has released a $15 checksum plugin for TunerPro that makes this process seamless.

http://www.mtx-electronics.com/automotive/page.php?25
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n00b
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« Reply #2 on: June 29, 2011, 10:52:02 AM »

Thanks. I was attempting to do thsi by hand with xdf values found in another thread for the 2.7TT box on my 1.8T HS code box.


I ended up doing a binary diff between files and poking around.

This saves much time, provided I can get a proper xdf.
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Low01Turbo
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« Reply #3 on: June 30, 2011, 07:21:42 AM »

Matt, Thanks so much for the  reply.  You cleared up some of my confusion.  Thanks for the link too.  I stumbled upon MTX before posting, but I wasn't quite meant what it all meant!

To be safe, if I modify the maps in anyway, I should be using a checksum corrector, right?
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Matt Danger
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« Reply #4 on: June 30, 2011, 10:09:08 AM »

To be safe, if I modify the maps in anyway, I should be using a checksum corrector, right?

Yes.
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vwaudiguy
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« Reply #5 on: July 02, 2011, 02:43:33 PM »

I was under the impression that the Tunerpro plugin was not able to correct checksums for 2002+ ME7 yet? What other options are there for these ecu's?
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"If you have a chinese turbo, that you are worried is going to blow up when you floor it, then LOL."
Low01Turbo
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« Reply #6 on: July 02, 2011, 03:09:55 PM »

There's ECUfix, but it's no where near the pricepoint of MTX.  Looks like a very worthwhile investment if you are going to be selling tunes to customers with custom setups, however.

http://www.ecufix.com/shop/index.php?main_page=product_info&cPath=2&products_id=180
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JulienR
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« Reply #7 on: November 22, 2018, 04:08:35 PM »

Checksums exist to verify the integrity of data and ensure the data has not changed. Your car's engine management system uses checksums to protect the engine components in the event the data on the ECU were to be corrupted or changed accidentally.

Checksums are embedded in the ECU file. The same model ECU will have the same checksum values, because the code on the ECU is the same. They are calculated using data in the file. The ECU contains a few different checksums, depending on the ECU model.

The ECU will recalculate some checksums every startup and compare the values to the one stored in the ECU. If they do not match the stored checksums it assumes data has been corrupted and will not allow the engine to start to prevent possible damage or other annoying things.

When you modify the ECU file you absolutely should recalculate the checksum values. This would be tedious if done by hand but fortunately for us MTX-Electronics has released a $15 checksum plugin for TunerPro that makes this process seamless.

http://www.mtx-electronics.com/automotive/page.php?25


are those checksums hardware related or software related ?
for example, if i choose to flash another software number to the same hardware number will that work ?
what i mean is does de ecu compare the checksum in the file with some other stored checksums elsewhere in the ecu ?

i have an 06a906032DR with hardware nr : 0261206887 and software nr : 1037360128
i've got a file from a friend also 06a906032DR same hardware number as mine but different software nr: 1037360272
(we both have the same engine : 1.8T AUM )

put both files in me7.x correction and both files where ok, is it possible to write that different software version and where can i see if the checksums are te same ?
or doens't they have to have the same checksums to work because you can use more possible checksums for the same ecu ?

Sorry for al the qeustions,  im trying to understand and learn
« Last Edit: November 22, 2018, 04:21:33 PM by JulienR » Logged
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