PapaSmurf2k3 wrote:On newer vehicles, the odometer on the dash shows what the vehicle thinks it actually has on it, whether that is stored in the cluster itself (rare), or in the Body Control Module (AKA "BCM" - more common).
I've never heard of someone being able to crack the BCM to roll the odometer back, but replacing it entirely might roll the odometer back to zero.
Actually, if its computer controled and stored its easy for someone to hack the odometer, once someone breaks the code. Go to the swap meet and chances are a guy with a laptop can do it in 10 minutes or so for 100 bucks. Jaguar has the mileage stored in 8 different places at random thinking hackers wouldnt be able to find all the different mileage recorded logs. Once the system was hacked they just asked the cars computer where the logs stored. Once the cars computers are changed, its virtually undetectable. At least with the mileage stored in the cluster, there's a chance of physical evidence the cluster was taken out of the car, lots of small delicate parts in some of these cars.
When its stored in the instrument cluster its a little more labor intensive but Pretty easy once the thing is taken apart, for a computer guy anyway.
The BCM, from what I've been told does not store or collect any data it basically just controls electronics. The ecu collects data, but doesnt comunicate with the dash cluster. I disconnected a cluster, drove approximately 30-40 miles and hooked it back up. I fully expected so see the 30-40 miles added to the total on the odometer, they weren't. I drove the car for another 20 or so miles right after hooking the cluster back up, the miles (30-40)never were added. I reset the trip odometer and 3000 miles later, they still werent added. If the miles are stored somewhere else in the car its very independent of the odometer on the dash.
Mileage is calculated and is stored in the cluster itself. There is a circuit board inside the instrument cluster and on this board there is an eprom, its kind of like a mini hard drive. The mileage is stored on that eprom. Every time the wheel rotates an electronic pulse is sent to the odometer and it is written onto the eprom. X revolutions of a wheel equals 1 mile thats is how the mileage is calculated on the odometer, at least for Nissans w/digital odometers '13 and earlier, most cars actually. There are 2 other ways mileage is calculated but i dont remember, both work the same way, count revolutions of something and send a pulse to the odometer. The eprom can be de soldered from the circut board, hooked up to a computer and rewriten with whatever mileage is desired. Resoldered to the circut board, put back in the cluster and reinstalled in the car. The car's odometer will then read whatever was written (burned) onto it. This is the only way to change the mileage on an odometer like that.
Now, there may very well be a secondary spot where mileage is stored, especially in newer cars but if there is, the odometer does not communicate with it, it is independent and a guarded secret. The is a code that shows if the mileage in tbe ecm and the odometer dont match, if the car doesnt store the mileage in the ecm, no code is thrown.
Why do i knowvall this? My son bought an 07 sentra, the odometer had 12k miles on it. Title says miles unkown, no record of anything at all with Nissian, nothing. Its was totaled out and Nissan said they must have dumped the records. The instrument panel is not new, yet it had 12000 miles. I was starting to think that the place my son got tje car from and Nissian were in collaboration.
I read quite a bit online trying to figure out how i could find the actual miles of the car. The only way I found was through sevice records, carfax had some but the last entry was an alignment at Pep Boys in '11 or ' 12 , @ 80k miles As far as I could tell, there is no other way to get the mileage, one service tech told me there might be something in the ecm's data or there might not and it would take a lot of time to sift through all the data and likely cost me 200-300 with no guarantee that they'd find anything, thats if the original ecm was in the car.
As far as a black box with mileage and other info, I don't think it exsists pre '14 anyway. I no nothing about 2014-present. The dealerships rely on the odometer, sevice records, carfax and title searches for mileage and discrepancies. Ive searched online, I've visited the dealership, I've asked people in other forums. No one has been able to tell definitively that mileage is stored in the cars computer, or that its not. Ive seen nothing that leads me to believe it is. Scary.
Do a web search, you will not find anyone say they found out their odometer was changed by hooking it up to a computer, Nissan anyway.
Good luck, if you find anything out please update, as you can tell I've been trying to figure this out myself.