GM Service Manual Online
For 1990-2009 cars
Makes 🢒 Chevrolet 🢒 2004 🢒 Tahoe - 4WD 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 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 be a powertrain performance condition present which could be a contributing cause to the customer's concern.

    2.

  2. This step is designed to identify engine-speed related disturbances that are NOT torque or load sensitive.

    3.

  3. This step is designed to identify engine-speed related disturbances that ARE torque or load sensitive.

    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.

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

Using a scan tool, determine if any DTCs are set.

Were any DTCs set?

Go to Diagnostic Starting Point - Engine Controls in Engine Controls - 4.8L, 5.3L, 6.0L, or Diagnostic Starting Point - Engine Controls in Engine Controls - 8.1L

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), still installed, start the engine.
  4. Place the transmission in NEUTRAL or PARK.
  5. Slowly increase the engine speed (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 obtained on the 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 brakes and the park brake.
  3. With the scan tool and the J 38792-A still installed, start the engine.
  4. Place the transmission in DRIVE.
  5. Slowly increase the engine speed (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 obtained on the J 38792-A .
  7. If no frequency data was obtained, attempt to obtain the frequency by placing the transmission into REVERSE, 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

Did 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 to the results of the same tests run, at the same engine RPM, on an equally-equipped, same model year and type, KNOWN GOOD vehicle. Refer to Vehicle-to-Vehicle Diagnostic Comparison .

  1. Install a scan tool into the known good vehicle.
  2. Install the J 38792-A into the known good vehicle; place the sensor in 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 speed (RPM) to the level at which the disturbance was most noticeable in the customer's vehicle.
  8. Record the engine RPM obtained on the scan tool and the most dominant frequency reading if obtained on the J 38792-A .
  9. Place the transmission in DRIVE.
  10. Slowly increase the engine speed (RPM) to the level at which the disturbance was most noticeable in the customer's vehicle.
  11. Record the engine RPM obtained on the scan tool and the most dominant frequency reading if obtained on the J 38792-A .
  12. If no frequency data was obtained, attempt to obtain the frequency by placing the transmission into REVERSE, then repeat steps 10 and 11.

Did both of the vehicles exhibit the same characteristics?

Go to Vibration Diagnostic Aids

Go to Vibration Analysis - Engine/Accessory Isolation