قطعة خاطئة أو تالفة رُكِّبت في إصلاح سابق

The right repair done with the wrong part, or the right part damaged while fitting it. It belongs on a diagnostic list because the timing gives it away and nothing else will — a fault that appeared with, or shortly after, work on the car is related to that work until proven otherwise.

Wheel speed measurement is where it bites most often. A hub or bearing with the wrong number of teeth on its tone ring, or with a magnetic encoder ring facing inward instead of outward, produces a wheel speed fault on a part that is new and undamaged. The encoder is easily wiped or scratched during pressing, and there is nothing to see afterwards.

Tyres are the other common one. A single replacement of a different size, or a space-saver left on, changes one wheel's rolling radius permanently — which the stability system reads as slip that never stops.

Ask what was done and when, before measuring anything. It is the cheapest question in diagnosis and it regularly answers the whole problem.