GM BCM programming how to calcualte checksums?

American Delco GM ECUs and PCMs, ALDL, OBD 1.5.
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GM BCM programming how to calcualte checksums?

Postby 04colyZQ8 » Sat Mar 18, 2017 4:24 pm

I can segment swap certain GM BCMs. I have a educated guess as to certain booleens are for, trouble is I can't figure out how to calculate the checksum (CVN) I've tried flashing without updated checksums and it bricks at 98%, but then is recoverable with GM SPS. The bins I have to don't show the CVns from GMs website? So I don't know they are calculating the checksums? It's likely some kind of CRC-16?

Here is a 2006 hummer H3 BCM stock lighting segment bin file. F2 E8 FA = the segment part number (15919354) Gm says the CVN is 0000E920 but I can't find that in the code, and I cannot calculate that value using 8, 16, CRC, so what gives? I'd guess the 08 D8 to be the checksum location (first 2 bytes) but I also can't figure out how that's calculated.

08 D8 00 03 00 F2 E8 FA 41 45 00 00 00 09 00 E0 04 02 46 AF 0D 00 00 68 90 00 00 44 14 00 00 18 04 11 00 00 00 00 00 00 01 FF F8 01 80 63 86 00 30 90 14 08 14 8D B8 00 C9 C0 A0 18 1A 01 0D 01 00 FF FF 00 19 FF FF 00 4C D1 D1 00 7F A3 A3 00 B2 75 75 00 E5 47 47 00 FF 47 47 00 3A 00 2F 00 00 59 A6 08 10 4D 15 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

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Re: GM BCM programming how to calcualte checksums?

Postby antus » Sun Mar 19, 2017 3:32 pm

Ive had a bit of a play, but came up empty. Do you have any ability to edit this file correctly and dump it again? Would be interesting to change one thing, preferably a single flag, and then dump it again. Should be able to zero in on what else changes that way. If the CVN isnt here, its also possible the sum isnt. Would also be beneficial to know what the sum is, better if we can see it in the file. Ive attached the file as a bin incase anyone wants to play with it in that format.
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Re: GM BCM programming how to calcualte checksums?

Postby typeigor » Wed May 08, 2019 10:10 pm

The checksum is stored in the first two bytes.
can be counted.

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