Diagnostic Procedure Overview

Qualifying the symptom by the particular sensation present can help narrow down the cause. Always use the "symptom" to "system" to "component" to "cause" diagnosis technique. This diagnostic method divides the problem into related areas to correct the customer concern.

• Verify the "symptom".
• Determine which "system(s)" can cause the "symptom" using the diagnostic tools described in this article.
  • If a vibration symptom is vehicle speed related, the tire and wheel rpm/frequency and driveshaft frequency should be calculated.
  • If a vibration symptom is engine speed related, the engine, engine accessory and engine firing frequencies should be calculated.
• After determining the possible "system(s)", refer to the appropriate article to identify the worn or damaged "components".
• After identifying the "components", identify the "cause" of the failure.

Remember that the vibrating source component (originator) may only generate a small vibration. This small vibration can in turn cause a larger vibration/noise to emanate from another receiving component (reactor), due to contact with other components (transfer path).

The diagnostic tools allow for a systematic collection of information that is necessary to accurately diagnose and repair NVH problems. For the best results, carry out the test as follows:

• Test drive the vehicle with the vibration sensor inside the vehicle.
• Place the sensor in the vehicle according to feel.
  • If the condition is felt through the steering wheel, the source is most likely in the front of the vehicle.
  • A vibration that is felt in the seat or floor only will most likely be found in the driveline, drive axle or rear wheels and tires.
• Record the readings. Also note when the condition begins, when it reaches maximum intensity and if it tends to diminish above/below a certain speed.
  • Frequencies with an amplitude reading of 0.06 Gs or less are barely perceptible NVH levels. No corrective action is necessary.
• Place the vibration sensor on or near the suspect area outside the vehicle.
• Continue the road test, driving the vehicle at the speed the symptom occurs, and take another reading.
• Compare the readings.
  • A match in frequency indicates the problem component or area.
  • An unmatched test could indicate the symptom is caused by the engine, torque converter or engine accessory. Use the diagnostic tools in the rpm mode and check if symptom is rpm related.