2005 Citroen C4

**blogon** · 28th September, 2020, 01:09 AM

Hey guys, trying to work out this citroen. Current reading is 367878 and I need 339000
Dash is 93c46 and Bsi is a johnston with a 95128.

**clusters** · 28th September, 2020, 01:30 AM

here.............

**blogon** · 28th September, 2020, 02:05 AM

Awesome, Thanks mate. Will give it a try.

**br556hre** · 28th September, 2020, 08:21 AM

sorry for bumping an old thread, but I'm curious.

Is there data about driven kilometres (or miles) stored on ECU?

Secondly how is this data from BSI been read to show 367.878 km on dash:

AA 55 09 DE BE 21 38 00
AA 55 DD DD EA 21 38 00
AA 55 C7 DD 00 22 38 00
AA 55 B2 DD 15 22 38 00
AA 55 9D DD 2A 22 38 00
AA 55 87 DD 40 22 38 00
AA 55 86 DD 41 22 38 00
55 AA 27 DE A0 21 38 00

To show 339.000 km bold bytes were all changed to same value: 9C 45 30 BA 33 ?

Anyone able to explain in simple terms how to interpret BSI raw data to read original 367.878 km and modified 339.000 km? - please share it!

**clusters** · 28th September, 2020, 04:21 PM

9c 45 is the complex CRC 30 ba 33 inverted to decimal = Km X 10

33 ba 30 = 3390000

**blogon** · 28th September, 2020, 10:34 PM

Hey, tried the files. Kms display correctly however vehicle will not start now, has an anti theft warning message.
Any ideas?

**br556hre** · 29th September, 2020, 01:12 PM

@blogon

:

Sorry to hear things went bad for you. Best you reflash with original data until you find solution.

You had 8 values changed in BSI, one of them was for sure not mileage (3rd line from my last post value 1437,0), other values are all slightly different but might be mileage.
My guess is slight differences in mileage have their meaning and shod have been changed respectfully.

@clusters: I think I'v been able to understand how CRC is calculated in this case:

data is: DD DD EA 22 38 00 for example 003822EA in decimal, divided by 10 is 367.895,4 km.

First two bytes are CRC check 32 bit data chunk (EA 22 38 00), it is calculated like this:
take the data chunk and xor it with FF FF FF FF, then take 1st byte add it to 3rd byte and subrtac result with 4th byte. Then the result is 1st byte of CRC, second one is 2nd byte od xoring result.

example, if data is EA 22 38 00 then CRC goes like this:

data Xor FF FF FF FF = 15 DD C7 FF
1ST BYTE + 3RD BYTE: 15 + C7 = DC
now result minus 4TH BYTE: DC - FF = DD
CRC = result of last step folowed by 2nd byte
CRC = DD DD.

Now complete message is CRC,data chunk:
DD DD EA 22 38 00
ta-da..