Dodge dealership in Canada is stating my old truck has 120k miles according to the ECM, whereas the odometer is showing 80k.

I had 35's on the truck but had the speedometer re calibrated within a week of putting them on. I am the second owner of the truck, owned since about 37k miles.

Please check my math:

Stock tires = 265 70 17 - 638 revs per mile
New tires = 315 70 17 - 587 revs per mile

638/587 = 1.09
1.09 * 80k miles = 87.2k miles

According to my math if the 35's were on there since mile 1 without a speedometer recalibration it would have been off by 7.2k miles.

How are they seeing a 40k difference? Could it be as simple as the Dodge techs in Canada giving data in kilometers verses miles? 80k miles is roughly 128k kilometers, a 48k difference.

How does the ECM get the mileage reading? Is that not what feeds the odometer in the dash? Does the back of the gauge cluster have the VIN for the vehicle on it?

Thanks guys -
Justin

 

Bump - anyone with insight?

 

The first owner probably unhooked the odometer for 40,000 miles. A guy showed me how to do it on a powerstroke (02 model) took him around 4 minutes. Some people have no Morals
I bet the ECM is right.

 

I knew the first owner of the truck. I was at the shop the day he bought it and I purchased it off him within 2 years. I'm not saying he didn't, but I would be very surprised if he did.

The odometer is digital anyway and receives a signal from the ECM I thought?

 

http://www.tirerack.com/tires/Spec.j...irePageLocQty=

Check this link out for revs per mile of a 315/70 r17 BFG.
I set mine to 601 rpm.

 

Thank you - that only further helps my point with the guy.

I still need to find out more about the ECM and odometer and how they interact. I wouldn't think you could disconnect a digital odometer and have it stop tracking the mileage. There has to be mirroring somewhere in the truck, they wouldn't have single points of failure, would they?

 

Yep the ECM is showing 120K....that is 120,000 KILOMETERS.....you have 80,000 MILES on your truck.....even though the ODO might show miles, the folks in canada read in KM's. 80,000 * 1.6 = 128,000 kilometers.....make sense?? and using your 1.09 calc.....128,000/1.09 = 117,500 kilometers.

 

Yeah, that's my point. Would the dealership be ignorant enough to tell the new owner that I jacked with the odometer because they are not taking into account the truck is an American truck and their data is given in kilometers?