Technical Service Bulletin SA-051-25 — 2018 MAZDA MAZDA3

Noise, Vibration, and Harshness (NVH) Diagnostic Guidelines Diagnostic Guidelines When diagnosing NVH concerns, it is essential to first classify the issue into one of three primary categories: Noise, Vibration, or Harshness. Many customer complaints may involve overlapping symptoms, such as both noise and vibration, so identifying the dominant characteristic is critical. Once the primary symptom is determined, follow the appropriate diagnostic path. For example, if a concern includes both noise and vibration but is related to vehicle speed, the vibration diagnostic path should be followed. When considering component replacement during the diagnostic process, it is best practice to start with the lowest cost or most accessible part unless diagnostic evidence clearly identifies a more expensive or complex component as the root cause. This approach helps minimize repair costs and avoids unnecessary part replacements. For example, a growling or bearing whine noise may be mistakenly attributed to internal components in the differential, transfer unit, or transmission, when the actual source is a wheel bearing. Misdiagnosis like this can lead to unnecessary repairs, added time and cost. To help prevent this, always follow the guidelines in the repair procedure.