Diagnostic Theory

The shortest route to an accurate diagnosis results from:
- System knowledge including comparison with a known good system.
- System history including repair history and usage patterns.
- Condition history, especially any relationship to service or sudden change.
- Knowledge of probable causes.
- Using a systematic diagnostic method that divides the system into related areas.

The diagnosis and correction of noise, vibration and harshness problems requires:
- A road test to determine the exact nature of the problem.
- An analysis of possible causes.
- Testing to localize the cause.
- Correcting any problems found.
- A road test to make sure the problem has been corrected.