کالیبراسیون نادرست دیفرانسیل یا لاستیک پس از تعمیر

A differential, gearbox or wheel-and-tyre package changed without the module's speed calibration being updated. The module derives road speed from rotation and a stored constant, so changing the gearing or the rolling radius makes every speed-derived value wrong by a fixed proportion.

The error is consistent rather than erratic, which is its signature and what separates it from a failing sensor: indicated speed, distance and every speed-dependent function drift by the same percentage in the same direction. A speedometer that reads a steady few percent out after a repair is this.

The consequences reach further than the speedometer. Shift points, cruise control, stability thresholds and the odometer all move together. Compare indicated speed against a satellite reference and calculate the ratio, which identifies it in one test. Many vehicles allow the constant to be configured, so correcting the calibration is usually the repair rather than reverting the change — and it must be done deliberately, since nothing prompts for it.