I read that the PCM tracks mileage for it's own purpose and BCM tracks and stores it for instrument cluster module to display it. So, when someone does an odometer/mileage correction, does it change the mileage value stored in the PCM or BCM or both?
Millage correction is possible on ALL vehicles and it does have its legal uses.
Peugeot/Citroen suffer from a bug where the BSI gets corrupt and the millage changes to a random value, Landrover 2005/07 to around 2014 also had a issue where if a instrument cluster was incorrectly programmed it would put 99999 miles on the clock.
Then there is obviously the cases where you need to program a second had instrument cluster or other module which contains millage data.
So now we get to the question, Which module gets changed?
Every manufacture is different.
Most VAG & Landrover vehicles it is only contained in the Instrument Cluster
PSA is contained in the BSI and the Instrument Cluster
Newer Mercedes have it stored in the ABS ecu and Instrument Cluster
I'll update the list when I have more time
When it comes to tools which change the millage there is not a single tool which will do every vehicle. The tools which cost a few thousand (and their clones found on auction sites) are never worth the money, the best option is to buy a decent universal programmer and take the small amount of extra time to disassembly the required module and hook up to the necessary memory IC directly.