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.

Did you review the Diagnostic Starting Point - Vibration Diagnosis?

Go to Step 2

Go to Diagnostic Starting Point - Vibration Diagnosis and Correction

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

Correct the faults before proceeding.

Did you correct the faults?

Go to Step 4

Do NOT operate the vehicle

Go to Step 2

4

1. Obtain the drive axles, final drive, ratios.
2. If the J 38792-VS Vibrate Software IS available, obtain the transmission gear ratios.
3. If the J 38792-VS is NOT available, take note of the tire size on each axle, then calculate the tire rotational speed for each size tire used and calculate the propeller shafts rotational speeds. Refer to Component Rotational Speed Calculation .

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

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1. Install a scan tool.
2. With the scan tool, bring up the Powertrain Control Module data list and select Engine Speed.

Is the scan tool operating properly?

Go to Step 6

Go to Scan Tool Does Not Communicate with Class 2 Device in Computer/Integrating Systems

Install the J 38792-A Electronic Vibration Analyzer (EVA) 2.

Is the J 38792-A operating properly?

Go to Step 7

Go to Electronic Vibration Analyzer (EVA) Description and Operation

Did the customer concern indicate that the vibration occurs ONLY while the vehicle is standing still?

Go to Vibration Analysis - Engine

Go to Step 8

8

1. Install the J 38792-A sensor to the component identified by the customer as most respondent to the vibration. If no component was identified, install the J 38792-A sensor to the steering column. You may have to move the sensor to other locations later.
2. Select a smooth, level road and slowly accelerate the vehicle up to highway speed.
3. Observe the vehicle for disturbances that match the customer description and note the following conditions:

•	The vehicle speed (km/h, mph)

•	The engine speed (RPM)

•	The transmission gear range and the specific gear

•	The vibration frequency reading, if detected by the J 38792-A

•	The feel and/or sound of the disturbance

4. If the vibration seems to excite a particular component of the vehicle more than the steering column, then move the J 38792-A sensor onto that component and repeat steps 2 and 3.

Were you able to duplicate the customer concern?

Go to Step 11

Go to Step 9

Is the vehicle equipped with four-wheel drive or all-wheel drive?

Go to Step 10

Go to Vibration Diagnostic Aids

1. With the J 38792-A sensor still installed in the same position, activate/engage all-wheel drive.
2. Select a smooth, level road and slowly accelerate the vehicle up to highway speed.
3. Observe the vehicle for disturbances that match the customer description and note the following conditions:

•	The vehicle speed (km/h, mph)

•	The engine speed (RPM)

•	The transmission gear range and the specific gear

•	The vibration frequency reading, if detected by the J 38792-A

•	The feel and/or sound of the disturbance

4. If the vibration seems to excite a particular component of the vehicle more than the steering column, then move the J 38792-A sensor onto that component and repeat steps 2 and 3.

Were you able to duplicate the customer concern?

Go to Step 11

Go to Vibration Diagnostic Aids

11

1. Accelerate the vehicle to a speed higher than the speed at which the disturbance occurs.
2. Shift the vehicle into NEUTRAL and allow the vehicle to coast down through the disturbance range.

Does the disturbance still occur while coasting-down in NEUTRAL?

Go to Step 13

Go to Step 12

12

1. Select a smooth, level road and slowly accelerate the vehicle up to the speed at which the disturbance occurs.
2. Decelerate and safely downshift by one gear range.
3. Operate the vehicle at the same VEHICLE SPEED at which the disturbance occurs.

Does the disturbance still occur while going the same vehicle speed in a lower gear range?

Go to Vibration Analysis - Driveline

Go to Vibration Analysis - Engine

Did the J 38792-A detect a dominant frequency?

Go to Step 14

Go to Symptoms - Vibration Diagnosis and Correction

1. If the J 38792-VS IS available, use the drive axles, final drive, ratios, the specific transmission gear ratio, and the engine speed to make a comparison to the dominant frequency reading recorded.
2. If the J 38792-VS is NOT available, compare the dominant frequency reading recorded to the component rotational data which you calculated previously.

Does the frequency data clearly fall within the tire/wheel parameters ONLY?

Go to Vibration Analysis - Tire and Wheel

Go to Step 15

Does the frequency data clearly fall within the propeller shaft parameters ONLY?

Go to Vibration Analysis - Driveline

Go to Symptoms - Vibration Diagnosis and Correction