GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2008 🢒 SLS 🢒 General Information 🢒 Vibration Diagnosis and Correction 🢒 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

Caution: One or more of the following guidelines may apply when performing specific required tests in the work stall:

   • When a test requires spinning the drive wheels with the vehicle jacked up, adhere to the following precautions:
      - Do not exceed 56 km/h (35 mph) when spinning one drive wheel with the other drive wheel stopped. This limit is necessary because the speedometer indicates only one-half the actual vehicle speed under these conditions. Personal injury may result from excessive wheel spinning.
      - If all of the drive wheels are spinning at the same speed, do not exceed 112 km/h (70 mph). Personal injury may result from excessive wheel spinning.
      - All persons should stay clear of the rotating components and the balance weight areas in order to avoid possible personal injury.
      - When running an engine in the repair stall for an extended period of time, use care not to overheat the engine and the transmission.
   • When a test requires jacking up the vehicle and running with the wheels and brake rotors removed, adhere to the following precautions:
      - Support the suspension at normal ride height.
      - Do not apply the brake with the brake rotors removed.
      - Do not place the transmission in PARK with the drive axles spinning.
      - Turn Off the ignition in order to stop the powertrain components from spinning.
   • When running an engine in the work stall, use the exhaust removal system to prevent breathing dangerous gases.

 

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