Diagnostic Theory

WARNING: This page is about a different car, the 2005 Mercury Montego, 2005 Ford Freestyle, and 2005 Ford Five Hundred. However, it is still accessible from the selected car via links, so may be relevant.

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.