Why is the odometer reading inconsistent with the actual mileage?

[ErinLee]

The reasons for the inconsistency between the odometer reading and the actual mileage include a faulty odometer sensor, issues with the wiring between the sensor and the dashboard, or a malfunctioning dashboard pointer. Generally, the latter has a very low probability of occurring and can be mostly ruled out. It is recommended that the driver visit a repair shop to have the odometer sensor checked and replaced if necessary. Determining whether the issue is with the sensor or the dashboard: Disconnect the sensor connector, turn on the ignition, and identify the 2nd electrode connected to the brown wire with a red stripe in the connector. Use a homemade wire with a plug to extend and lightly brush against a grounded part of the vehicle body to input a pulse signal to the dashboard. If the speedometer needle moves, it indicates the dashboard is functioning properly. The fault lies in the sensor's reed switch or magnetic ring. If the speedometer needle does not move, it suggests an issue with the dashboard or the connecting wiring. Determining whether the issue is with the dashboard or the wiring: Remove the dashboard without unplugging the connector, and use a multimeter to measure the three electrodes on the dashboard. Turn on the ignition, and the voltage from fuse No. 26 to the power line of the speedometer/odometer should read 12V when measured against the ground. Use the multimeter's resistance mode to measure the pulse signal line from the dashboard to the sensor connector; the resistance should be zero, and the ground electrode's resistance to the ground should also be zero. If the actual measurements do not match these three values, any short circuits in the wiring should be addressed. If the wiring is found to be fault-free, the issue lies with the speedometer/odometer, which should be repaired or replaced as needed.

[Hunger]

I've encountered this situation many times. It mainly depends on whether the tire size has been changed. For example, if the original 215 tires were replaced with 235 ones, the altered tire circumference would make the speed sensor inaccurate. Other factors like driving on severely worn tires without replacement, or consistently underinflated tires, can easily cause the odometer to deviate by 20,000-30,000 km from actual mileage. If the tires haven't been modified, the speed sensor is likely the culprit - that little component near the transmission is prone to water damage and rust. Last time mine malfunctioned after driving through water during rain. Additionally, aging circuit boards in older vehicles or odometer tampering could be causes. I recommend using an OBD scanner to read the engine's actual mileage for comparison.

[TeaganRose]

Let's start with the vehicle's signal transmission path. The wheel speed sensor collects the wheel rotation signal and sends it to the ECU, which then transmits it to the dashboard for display. The most prone to failure is the magnetic ring part of the sensor—it can go haywire if contaminated with iron filings or dampness. Another common issue is a loose sensor connector on the rear axle differential; poor contact after vehicle jolts can cause the odometer to jump erratically. I once repaired an off-road vehicle where the owner reported the dashboard showing 20,000 kilometers less than actual mileage—turned out the sensor wiring harness was disturbed during shock absorber modification, causing signal attenuation. Also, pay attention to the onboard computer software version; some older vehicles may show discrepancies after system upgrades if proper calibration isn't performed.

[LaPreston]

There are generally three common scenarios: either it's a tire issue, such as replacing tires with non-original sizes or incorrect tire pressure, causing a discrepancy between the actual rolling distance and the sensor's calculation; or it's a problem with the vehicle speed sensor, which is located near the transmission and is particularly prone to malfunction due to oil contamination; or the odometer has been tampered with, which is especially common in used cars. However, odometer tampering usually only alters the dashboard display, while the actual mileage is still stored in the engine's computer. Using professional equipment to check ECU data can reveal the truth. I recommend first using a tire pressure gauge to measure the pressure in all four tires, and then checking the maintenance records to see if any chassis components have been recently serviced.