The numbers below refer to the step numbers on the diagnostic table.
Obtaining rotational speed for the components rotating at tire/wheel speed is critical to systematically eliminating specific vehicle component groups. These component rotational speeds can be generated by using the J 38792-VS Vibrate Software, or through calculating them manually.
Important: Be certain to OBSERVE for disturbances that match the customer description FIRST, then look at the J 38792-A Electronic Vibration Analyzer (EVA) 2 frequency which corresponds with that disturbance.
Proper location of the J 38792-A sensor onto the component which is most excited by the vibration disturbance is critical to obtaining an accurate frequency reading.
This test will duplicate virtually any disturbance which occurs while the vehicle is in motion.
Accelerate to a speed high enough above the speed of the disturbance to allow for the time needed to shift into NEUTRAL and for the engine to decrease in RPM to idle speed, before coasting down through the disturbance range.
This test will either eliminate or confirm the engine as a contributing cause of the customer concern.
Step | Action | Yes | No | ||||||||||
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Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage. | |||||||||||||
1 | Did you review the Diagnostic Starting Point - Vibration Diagnosis? | Go to Step 2 | Go to Diagnostic Starting Point - Vibration Diagnosis and Correction | ||||||||||
2 | Visually inspect the tire and wheel assemblies, steering components, and suspension components for any possible faults. Are the tire and wheel assemblies, steering components, and suspension components in good working condition? | Go to Step 4 | Go to Step 3 | ||||||||||
3 |
Important: Do NOT operate the vehicle until the faults are corrected. Correct the faults with the tire and wheel assemblies, steering components, and/or the suspension components before proceeding . Did you correct the faults with the tire and wheel assemblies, steering components, and/or the suspension components? | Go to Step 4 | Go to Step 2 | ||||||||||
Did you obtain the powertrain ratios for use with the J 38792-VS , or calculate the component rotational speeds, if J 38792-VS is NOT available? | Go to Step 5 | -- | |||||||||||
5 |
Is the scan tool operating properly? | Go to Step 6 | Go to Diagnostic Starting Point - Computer/Integrating Systems in Computer/Integrating Systems | ||||||||||
6 | Using the J 38792-A Electronic Vibration Analyzer (EVA) 2 is the preferred method for gathering necessary vibration frequency data. If the J 38792-A is not available, the necessary vibration frequency data will have to be obtained based on symptoms observed during testing. Review Symptoms - Vibration Diagnosis and Correction to become familiar with the possible frequency ranges. Review Symptoms - Vibration Diagnosis and Correction, as necessary throughout the remainder of diagnostics. Is the J 38792-A available for use? | Go to Step 7 | Go to Step 8 | ||||||||||
7 | Install the J 38792-A . Is the J 38792-A operating properly? | Go to Step 8 | Go to Electronic Vibration Analyzer (EVA) Description and Operation | ||||||||||
8 | Did the customer concern indicate that the vibration occurs ONLY while the vehicle is standing still? | Go to Step 9 | |||||||||||
Were you able to duplicate the customer concern? | Go to Step 10 | ||||||||||||
Important: If the vehicle is equipped with an automatic transmission, let the vehicle coast to a stop before shifting back into gear. Does the disturbance still occur while coasting-down in NEUTRAL? | Go to Step 12 | Go to Step 11 | |||||||||||
Does the same disturbance still occur while going the same vehicle speed in a lower gear range? | |||||||||||||
12 | If the J 38792-A is not available, refer to Symptoms - Vibration Diagnosis and Correction . Did the J 38792-A detect a dominant frequency? | Go to Step 13 | |||||||||||
13 |
Does the frequency data clearly fall within the tire/wheel parameters ONLY? |