NVH Diagnosis Basics
A structured approach to noises and vibrations instead of guesswork.
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What you will learn
- Classify noises by condition
- Use the vehicle condition to narrow causes
- Confirm the source
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Noise, vibration and harshness (NVH) complaints are best attacked by recording exactly when they happen: cold or hot, at idle or a specific speed, in gear or neutral, braking or turning, on load or coasting. That pattern narrows the possible sources dramatically.
Then isolate. Changing one variable at a time — gear, load, speed, steering angle — shows whether the source is engine, transmission, drivetrain, wheel or body. A stethoscope, a second technician and a test drive are professional tools, not tricks.
| Condition | Likely area |
|---|---|
| Follows engine speed at standstill | Engine/accessory |
| Follows road speed | Wheels, tyres, drivetrain |
| Only when turning | Suspension, differential, bearings |
| Only when braking | Brakes, discs, run-out |
| Only when cold | Belts, clearances, oil |
Key points
- The conditions of the noise are the diagnosis.
- Change one variable at a time to isolate.
- Confirm the source before replacing parts.
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Key points
- When it happens is the key clue
- Speed, load, temperature and gear matter
- Isolate by changing one variable at a time
All values shown are training examples. Real thresholds depend on the manufacturer, engine, temperature and system — always confirm with the vehicle service documentation.
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