What are the reasons for the discrepancy between the odometer reading and the actual mileage?
5 Answers
The reasons for the discrepancy 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 usually be ruled out. It is recommended that the driver visit a repair shop to have the odometer sensor inspected and replaced if necessary. Determining whether the issue is with the sensor or the dashboard: Disconnect the sensor connector, turn on the ignition, and locate the 2nd electrode connected to the brown wire with a red stripe in the connector. Use a homemade wire with a plug to extend it 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 that the dashboard is functioning properly. The fault lies with 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 disconnecting the plug, and use a multimeter to measure the three electrodes on the dashboard. Turn on the ignition, and check that the voltage from fuse No. 26 to the power supply line of the speedometer should be 12V when measured against the ground. Use the multimeter's resistance mode to measure; the resistance of the pulse signal line from the dashboard to the sensor connector should be zero, and the resistance of the ground electrode 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 confirmed to be fault-free, the issue lies with the speedometer, which should be repaired or replaced as needed.
I've been driving for over a decade and have encountered situations where the odometer reading doesn't match the actual mileage several times. This mainly happens when the system isn't properly calibrated after tire changes, such as installing larger or smaller tires. The dashboard sensors get confused because they calculate mileage based on wheel speed, causing the displayed distance to differ from the actual distance traveled. Another issue is sensor malfunctions—for example, speed sensors or odometer sensors may report incorrect data due to moisture damage or aging. Once, after my car got waterlogged, the dashboard started acting erratically after rain, and it turned out to be a short circuit in the electrical wiring. Another factor is tampering during repairs, such as when a repair shop accidentally resets the system or manipulates data using diagnostic tools—don't doubt it, this happens often, especially when buying used cars, so be wary of odometer fraud. In short, this issue not only affects fuel estimation but can also mislead maintenance schedules, posing safety risks. It's best to visit a professional shop early and diagnose it with an OBD scanner tool.
I'm a new car owner and recently noticed the odometer reading doesn't match my phone's navigation records - it's significantly undercounting. This might be due to a mistake during maintenance, like when the technician accidentally reset the data during the last service, or an error occurred when connecting diagnostic tools to the car's computer. Additionally, aging vehicle sensors can cause such discrepancies. My friend's old car had a faulty wheel speed sensor, causing the odometer to undercount - showing only 80 km when actually driving 100 km. This issue can also relate to tire replacement since the odometer relies on wheel speed sensors for calibration. If new tires are installed without proper ratio adjustment, distance calculations become inaccurate. I find this quite annoying as it directly affects maintenance reminders and fuel consumption statistics, so regular inspection of the wiring system is necessary. If you discover inaccurate mileage readings only when going on a long trip, it could cause major trouble. It's best to address this promptly.
I think the main reasons are sensor issues or electronic faults—the vehicle's dashboard relies on sensors to collect wheel speed for mileage calculation. If the wheel speed sensor malfunctions, such as being damaged by water ingress or having poor contact, signal reception failure will display incorrect mileage. Similarly, errors in the car's computer software can also cause data mismatches, which are particularly common after rainy days or on bumpy roads. Additionally, if the tire size is changed without resetting the parameters, the mileage ratio will be incorrect. This issue needs to be fixed promptly, otherwise it will affect safety assessments.
As an ordinary office worker, I drive to and from work every day and have noticed that when the odometer reading suddenly doesn't match the actual mileage, it's often due to external factors like not properly calibrating the wheel speed sensor after changing tires, leading to calculation errors. It could also be internal issues such as a faulty sensor or aging wiring. This can cause trouble, like inaccurate maintenance records affecting warranty rights—I once went to the dealer, and they said the mileage discrepancy was due to modifications, nearly refusing free service. Additionally, during post-accident repairs, technicians might accidentally alter the vehicle's computer data, causing inconsistencies. I think it's important to develop a habit of regular checks, using simple tools like an OBD adapter connected to a phone app to verify the mileage.
