For 1990-2009 cars

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. 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.

2. Important: Be certain to OBSERVE for disturbances that match the customer's description FIRST, then look at the J 38792-A frequency which corresponds with that disturbance.

   Proper location of the J 38792-A Electronic Vibration Analyzer (EVA) 2, 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.

3. 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.

4. This test will either eliminate or confirm the engine as a contributing cause of the customer concern.

Step | Action | Yes | No
--- | --- | --- | ---
Caution: Refer to Road Test Caution in the Preface section.
1 | Did you review the Diagnostic Starting Point - Vibration Diagnosis? | Go to Step 2 | Go to Diagnostic Starting Point - Vibration Diagnosis and Correction
2 | Did the customer concern indicate that the vibration occurs ONLY while the vehicle is standing still? | Go to Step 6 | Go to Step 3
3 | 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 5 | Go to Step 4
4 | 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 5 | Go to Step 3
5 |

1. Obtain the drive axle final drive ratio.
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 shaft rotational speed, if equipped. 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 6

--

6 |

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 7

Go to Diagnostic System Check - Vehicle

7 | 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 8

Go to Step 9

8 | Install the J 38792-A . Is the J 38792-A operating properly? | Go to Step 9 | Go to Electronic Vibration Analyzer (EVA) Description and Operation
9 | Did the customer concern indicate that the vibration occurs ONLY while the vehicle is standing still? | Go to Vibration Analysis - Engine | Go to Step 10
10 | Did the customer concern indicate that the vibration occurs ONLY during heavy acceleration at launch? | Go to Step 11 | Go to Step 14
11 |

1. Install the J 38792-A sensor, if available, to the pinion area of the drive axle. Route the sensor lead wire clear of rotating parts and loosely secure the wire clear of moving parts. If it is not possible to install the J 38792-A sensor, if available, to the drive axle, install the sensor to an exposed portion of the floor panel or seat track in the area that the customer noted is most respondent to the vibration.
2. Select a smooth, level road.
3. With the vehicle at a stand-still, apply the regular brake and place the transmission in the lowest forward gear.

Important: Do not accelerate to the point of causing the drive wheels to squeal, slip or hop - this would obscure the results of the test.

4. Release the regular brakes and accelerate aggressively to 32 km/h (20 mph).
5. Observe the vehicle for disturbances that match the customer's description and note the following conditions:

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

• | The feel and/or sound of the disturbance

6. If a reading could not be obtained by the J 38792-A , move the J 38792-A sensor, if available, to another part that is respondent to the vibration and repeat steps 3-5.

Were you able to duplicate the customer's concern?

Go to Step 12

Go to Step 14

12 | Is the vehicle primary driveline configuration rear wheel drive? | Go to Step 13 | Go to Step 14
13 | Is the vehicle equipped with a solid drive axle? | Go to Vibration Analysis - Driveline | Go to Vibration Analysis - Hub and/or Axle Input
14 |

1. Install the J 38792-A sensor, if available, to the component identified by the customer as most respondent to the vibration. If no component was identified, install the J 38792-A sensor, if available, 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's description and note the following conditions:

• | The vehicle speed

• | The engine 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, if available, onto that component and repeat steps 2 and 3.

Were you able to duplicate the customer's concern?

Go to Step 17

Go to Step 15

15 | Is the vehicle equipped with selectable four-wheel or all-wheel drive? | Go to Step 16 | Go to Step 17
16 |

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's description and note the following conditions:

• | The vehicle speed

• | The engine 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, if available, onto that component and repeat steps 2 and 3.

Were you able to duplicate the customer's concern?

Go to Step 17

Go to Vibration Diagnostic Aids

17 |

1. Accelerate the vehicle to a speed higher than the speed at which the disturbance occurs.

Important: If the vehicle is equipped with a continuously variable type automatic transmission, let the vehicle coast to a stop before shifting back into gear.

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 19

Go to Step 18

18 |

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

Go to Vibration Analysis - Hub and/or Axle Input

Go to Vibration Analysis - Engine

19 | 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 20 | Go to Symptoms - Vibration Diagnosis and Correction
20 |

1. If the J 38792-VS IS available, use the drive axle final drive ratio, the specific transmission gear ratio, and the engine RPM 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 21

21 | Does the frequency data clearly fall within the propeller shaft parameters ONLY? | Go to Vibration Analysis - Driveline | Go to Step 22
22 | Is the vehicle equipped with a solid drive axle? | Go to Symptoms - Vibration Diagnosis and Correction | Go to Vibration Analysis - Hub and/or Axle Input