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 probable causes.
^ 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 a acceptable range.

Diagnostic Process







NHV Diagnostic Procedure - Noise and Harness







NHV Diagnostic Procedure - Vibration

A good diagnostic process is a logical sequence of steps that lead to the identification of a causal system. The flowcharts are a graphic representation of the diagnostic process. Use the flowcharts as follows:
^ Choose the appropriate flowchart.
^ Identify the operating condition that the vehicle is exhibiting.
^ Advance through the flowchart from left to right
^ Match the operating condition to the symptom.
^ Verify the symptom.
^ Identify which category or system could cause the symptom.
^ Refer to the diagnostic symptom chart that the flow chart refers to. Symptom Charts