Ford 2003 Mustang Workshop Manual page 33

SECTION 100-04: Noise, Vibration and Harshness
DESCRIPTION AND OPERATION
Noise, Vibration and Harshness (NVH)
Noise is any undesirable sound, usually unpleasant in nature. Vibration is any motion, shaking or
trembling, that can be felt or seen when an object moves back and forth or up and down. Harshness is
a ride quality issue where the vehicle's response to the road transmits sharply to the customer.
Harshness normally describes a firmer than usual response from the suspension system. Noise,
vibration and harshness (NVH) is a term used to describe these conditions, which result in varying
degrees of dissatisfaction. Although, a certain level of NVH caused by road and environmental
conditions is normal. This section is designed to aid in the diagnosis, testing and repair of NVH
concerns.
Acceptable Noise, Vibration and Harshness
All internal combustion engines and drivelines produce some noise and vibration; operating in a real
world environment adds noise that is not subject to control. Vibration isolators, mufflers and dampers
reduce these to acceptable levels. A driver who is unfamiliar with a vehicle can think that some sounds
are abnormal when actually the sounds are normal for the vehicle type. For example, Traction-Lok®
differentials produce a slight noise on slow turns after extended highway driving. This is acceptable
and has no detrimental effect on the locking axle function. As a technician, it is very important to be
familiar with vehicle features and know how they relate to NVH concerns and their diagnosis. For
example, if the vehicle has automatic overdrive, it is important to test drive the vehicle both in and out
of overdrive mode.
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 repairs or sudden change.
knowledge of possible sources.
using a systematic diagnostic method that divides the system into related areas.
The diagnosis and correction of noise, vibration and harshness concerns requires:
a road or system test to determine the exact nature of the concern.
an analysis of the possible causes.
testing to verify the cause.
repairing any concerns found.
a road test or system test to make sure the concern has been corrected or brought back to
within an acceptable range.
Glossary of Terms
2003 Mustang Workshop Manual