How to Calibrate an Inaccurate Speedometer?
2 Answers
Speedometer calibration methods vary by vehicle model, so it is recommended to have it performed by professionals at a 4S dealership. The speedometer displays the vehicle's speed in either miles per hour or kilometers per hour, with speed measurement achieved through a speed sensor. The vehicle's speed is closely related to wheel radius and axle structure. There are two main reasons why a car speedometer may display a higher value than the actual speed: safety considerations and calculation errors. China's roads have maximum speed limits based on accident statistics and road conditions to prevent speeding and overtaking. Additionally, onboard speed measurement devices may have delays, so displaying a higher value than the actual speed helps prevent sudden acceleration hazards.
I've been driving for decades and have seen many cases of inaccurate speedometers. The most common cause is changing to tires of different sizes. Incorrect tire pressure, whether too high or too low, can also affect the readings, so first check if the tire pressure and wheel specifications match the factory settings. For a simple verification, find a straight road section and compare with a mobile GPS speed measurement app. If the error is significant, action needs to be taken. You can clean the wheel speed sensors yourself to remove mud or corrosion, but calibration requires professional tools to connect to the OBD port and reset the ECU data. It's best to go to a 4S shop or repair station, as they have specialized equipment to calibrate the sensors safely and reliably. Don't delay, as an inaccurate speedometer can easily lead to speeding tickets or accidents.
