pcmhacking.net

O.k. after looking at checksum's for other stuff I thought I'd start with something simple as it's a lot smaller for example the file attached I believe the checksum is 16Bit stored at $00D4 $00D5 but how does it come to that F0 0F, what parts is it including & what calculation does it use?

So I thought without any responses maybe it's too hard to do checksums without knowing more about it, but thought I'd keep looking anyway.

So in Hex Workshop it doesn't show anything like what is supposed to be the checksum, in attached screenshot the CKS should be B24D which is at $00D4 & $00D5 again but do you include that or exclude(I've tried both ways & still doesn't add up) so I thought it must be a custom CRC16 & just tried different values in each of the box but really don't know what I'm testing... is there a general of each of the boxes thats common for most sums?

How do you know or why do you think the checksum is at that location?? The location has always been excluded from the checksum in my experience..

my experience is limited and to ecms.. Sometimes there's 2 checks, a checksum and a crc-16.. usually crc is first excluding the crc location AND excluding the checksum.. crc is written in and then the checksum is done excluding only the checksum locations..

I'm only assuming the checksum is at that location as when the file is modified everyone else just zero's both those bytes & been told thats the checksum in numerous forums but work around is to just zero it but I thought it would be an easy file to start with figuring checksums.

That file looks like eeporm dump to me. It have some vin look alike part and some other identifiers typical for eeprom. There is at least 5-6 different p/n in hex scattered in the file.

I guess that zeroing of the bytes is not actual checksum but bit encoded stuff to disable checksums. Do you have more dumps to look at with corresponding vins, some patterns can be found. Or a full dump with code and info for processor being used.

Yeah I have 20 or more of the dumps, some from earlier model but same style that only have 1KBf size & later have 2KB size....
I’ll dig some out!

O.k. so I just grabbed 10 quickly, some are 2KB & some are 1KB....

Well, those bytes do look to be an 8-bit checksum, as they're a one's complement of each other.

Joe.

What hex editor are you using?? Looks interesting, I'm using neo and it's working ok but yours looks interesting..

I did some preliminary digging and almost figured the file structure.

Too bad I cant find a gm files to confirm start-end of segment. ALso not sure if there is some missing data.

Here is some of the dumps. There is a chance that there is multiple checksums or only one.

DUMP 8

Module Part Number CVN
Operational Software 92260731 Unknown
Fuel Calibration 92226843 0000D7F6
Service Calibration 92226842 0000E5D6
Temperature Map 92226837 0000E4EC
DTC Calibration 92234355 000028DB

VIN: 6G1EK8EV59L333437

and

DUMP 5 6
$34
$42 PN ONLY
$48 VIN
$5E

Operational Software 92262631 Unknown 057FD0E7
Fuel Calibration 92254799 Unknown 057FB24F $150
Service Calibration 92226842 0000E5D6 057F451A $117
Temperature Map 92247713 0000234F 057F96A1 [A0]$83
DTC Calibration 92244999 00008166 057F8C07 $1A4

VIN: 6G1EK8EV5BL547734

Part of the vin is also in the file.

If anyone can source some of these p/n figuring the rest will be easy.


VX L67 Getrag do you know if these files are stock dump or modified.