GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2009 🢒 SLS 🢒 Preface 🢒 Dangers, Warnings, and Cautions 🢒 Vibration Analysis - Engine

Test Description

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

  1. If powertrain related DTCs are present, there may exist a powertrain performance condition which could be a contributing cause to the customer's concern.

    2.

  2. This procedure is used to determine the disturbance related to engine RPM and not sensitive to the torque or load.

    3.

  3. This procedure used to determine the vibration disturbance related to engine RPM and sensitive to the torque or load.

    4.

  4. Making comparisons of the customer's vehicle with an equally equipped, same model year and type, KNOWN GOOD vehicle will help determine if certain disturbances may be characteristic of a vehicle design.

Vibration Analysis - Engine

Step

Action

Yes

No

Warning: Refer to Work Stall Test Warning in the Preface section.

 

1

Has the Vibration Analysis - Road Testing table been completed?

Go to Step 2

Go to Vibration Analysis - Road Testing

2

Use a scan tool to determine if any DTCs are set.

Is there any DTC set?

Go to Diagnostic Starting Point - Engine Controls

for the 3.6L (LY7) engine

or

Go to Diagnostic Starting Point - Engine Controls for the 4.6L (LH2) engine

Go to Step 3

3

  1. Block the front wheels.
  2. Apply BOTH the service brakes and the park brake.
  3. With the scan tool and the J 38792-A , Electronic Vibration Analyzer (EVA) 2, if equipped, still installed, start the engine.
  4. Place the transmission in NEUTRAL or PARK.
  5. Slowly increase the engine RPM to the level at which the disturbance is most noticeable.
  6. Record the engine RPM obtained on the scan tool and the most dominant frequency reading if data is obtained from J 38792-A .

Were you able to duplicate the customer's concern?

Go to Step 5

Go to Step 4

4

  1. Block the front wheels.
  2. Apply BOTH the service brake and the park brake.
  3. With the scan tool and J 38792-A still installed, start the engine.
  4. Place the transmission in DRIVE.
  5. Slowly increase the engine RPM to the level at which the disturbance is most noticeable.
  6. Record the engine RPM obtained on the scan tool and the most dominant frequency reading if data is obtained from J 38792-A .
  7. If no frequency data was obtained, attempt to place the transmission into REVERSE to obtain the frequency, and then repeat steps 5 and 6.

Were you able to duplicate the customer's concern?

Go to Step 5

Go to Vibration Diagnostic Aids

5

Does the J 38792-A detect a dominant frequency?

Go to Step 6

Go to Symptoms - Vibration Diagnosis and Correction

6

Compare the test results of the customer's vehicle with the results of the same tests run, at an equally-equipped, same model year and type, KNOWN GOOD and same engine RPM vehicle. Refer to Vehicle-to-Vehicle Diagnostic Comparison.

  1. Install a scan tool into the known good vehicle.
  2. Install J 38792-A into the known good vehicle and place exactly the same location as it was placed in the customer's vehicle.
  3. Block the front wheels.
  4. Apply BOTH the service brakes and the park brake.
  5. Start the engine.
  6. Place the transmission in NEUTRAL or PARK.
  7. Slowly increase the engine RPM to the level at which the disturbance is most noticeable in the customer's vehicle.
  8. Record the engine RPM obtained on the scan tool and the most dominant frequency reading if data is obtained from J 38792-A .
  9. Place the transmission in DRIVE.
  10. Slowly increase the engine RPM to the level at which the disturbance is most noticeable in the customer's vehicle.
  11. Record the engine RPM obtained on the scan tool and the most dominant frequency reading if data is obtained from J 38792-A .
  12. If no frequency data was obtained, attempt to obtain the transmission into REVERSE to obtain the frequency, and then repeat steps 10 and 11.

Did both vehicles exhibit the same characteristics?

Go to Vibration Diagnostic Aids

Go to Vibration Analysis - Engine/Accessory Isolation