Inaccurate Calibration
One of the most common reasons for inaccurate speedometer readings is incorrect calibration. During production or after repairs, the speedometer must be calibrated to accurately measure the vehicle’s speed. If the calibration is wrong, the speedometer will display a higher or lower speed than the actual speed.
Damaged Speed Sensor
The speed sensor is a crucial element in the speed measurement system. This sensor, usually located in the transmission or on the wheel, sends a signal to the vehicle’s computer about the wheel rotation speed. If the sensor is damaged or dirty, the signal may be distorted, leading to an inaccurate speedometer reading. Symptoms of a damaged sensor may include erratic speed readings, speedometer needle flickering, or complete speedometer failure.
ABS or Vehicle Computer Problems
In modern vehicles, the speedometer is often connected to the ABS (Anti-lock Braking System) and the vehicle computer. Malfunctions in these systems can affect the accuracy of the speedometer reading. For example, a problem with an ABS sensor can lead to an incorrect speed display. Checking diagnostic trouble codes using a diagnostic tool can reveal problems in these systems.
Wiring Problems
Damaged or loose wiring between the speed sensor, the vehicle computer, and the speedometer can cause erratic readings. Corrosion, damage from rodents, or simply poorly connected connectors can interrupt the signal, resulting in inaccurate or inconsistent speed display.
Mechanical Problems with the Speedometer
In older vehicles, the speedometer is a mechanical device. Over time, mechanical parts can wear out or become damaged, which can lead to inaccurate readings. The problem could be in the needle itself, the gears, or the cable connecting the transmission to the speedometer.
Pneumatic Systems (in some vehicles)
Some older trucks and other vehicles use pneumatic systems to measure speed. Air leaks in the system can affect the accuracy of the speedometer reading.
What to do if you have problems with your speedometer?
If you notice that your speedometer is inaccurate, it is recommended to visit a qualified mechanic to determine the cause of the problem and perform the repair. Neglecting the problem can lead to more serious malfunctions and potentially dangerous situations in traffic.