سایش چرخ‌دنده محرک کیلومترشمار

The mechanical drive gear taking speed from the gearbox, worn so its teeth slip or its signal becomes irregular. It applies to designs that still use a driven sensor rather than reading a toothed wheel directly, and the gear is often a plastic part meshing with a metal one.

Wear produces a signal that is intermittent or reads low rather than absent, so the module receives a plausible speed that is wrong — and speed feeds the transmission's shift points, cruise control and the stability systems. A speedometer that reads low and flickers is the direct symptom.

Plastic gears strip in a way that is obvious once inspected, and the debris is a useful indicator of how long it has been failing. Check the gear rather than the sensor, since the sensor is the part usually replaced and is frequently fine. A gear that has stripped will have shed material into the gearbox, so it is worth checking where the fragments went.