True Odometer Readings: The Key to Tax Compliance
In modern vehicles, computerized odometers are commonplace and are implemented by counting the number of times complete wheel revolutions are detected by one or many sensors. Vehicle computers then factor in the drive axle ratio and average wheel diameter to approximate the distance traveled by a vehicle. Wheel diameter can vary due to temperature, tire inflation, and tread thickness. This leads to accuracy errors in odometer readings displayed on a vehicle dashboard and in between different systems on the same vehicle when compared to detailed distance calculations using GPS and mapping technology.
There are also a number of reasons why there is a discrepancy between an electronically readable odometer obtained by a telematics device and the odometer presented on the dashboard.
1. Multiple subsystems with independent odometers: Multiple subsystems can and will maintain independent versions of the odometer. At any given moment, several systems within a vehicle are counting these clicks and converting them to a distance. For example, the powertrain control module (PCM), transmission control module (TCM), and the instrument panel cluster (IPC) often maintain their own independent counts of the number of wheel revolutions detected.
2. Conversion error and conversion accuracy: Odometer readings are maintained in various units and resolutions. We commonly see 0.1 km, 1 km, 0.1 mile, 1 mile, 1/64 of a mile, etc. Some OEMs also have a less accurate way to convert odometer readings from kilometers to miles or vice versa and there is variation between the same vehicle's systems. This conversion error is not very apparent in new vehicles but grows once the vehicle has significant mileage.
3. Replaced or Repaired components: Some vehicles have had their computer systems replaced or re-flashed (reprogrammed). In many cases, the odometer setting in the replaced or reflated system is not correctly adjusted to the current value. This leads to a large variance between what is displayed on the dashboard and what is provided to various other systems.
4. Swap-outs and repurposed components from donor/salvage vehicles: While less common, wholesale swap outs of dashboards, PCMs, and or TCMs occur, and the odometer and/or VIN number information of the donor vehicle is left as-is and also causes a large variance between displayed and reported odometer data.
5. The instrument cluster inaccessible through the diagnostic port: In many cases, the instrument cluster/dashboard is inaccessible through the diagnostic port and also maintains a separate free-running odometer that is different from that available through the diagnostic port. This also leads to a difference in what is displayed on the dashboard and what is available to report electronically.
On light duty vehicles, the OBD standards do not require that the odometer displayed on the dashboard be reported. Consequently, the vast majority of light duty vehicles do not have any agreed upon method to do so. LynX has implemented a number of proprietary methods to determine odometer readings from these vehicles wherever possible.
Among heavy duty vehicles, protocols such as J1939 and J1708 are common and provide for the ability to report odometer readings electronically. While not required, most vehicle manufacturers choose to implement the feature. On these vehicles, telematics devices might have access to the instrument cluster at the discretion of the manufacturer. This access can vary for each manufacturer from year to year and between models of the same year.
In both cases, LynX devices attempt to discover all sources of electronic odometer readings available and then prioritize the odometer readings that are most likely visible to the driver and displayed on the dashboard.
-Manish Desai