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Test Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

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

  1. 2:  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. 3:  This step is designed to identify engine-speed related disturbances that are NOT torque or load sensitive.
  3. 4:  This step is designed to identify engine-speed related disturbances that ARE torque or load sensitive.
  4. 6:  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: Refer to Work Stall Test Caution in Cautions and Notices.
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 - 4.3L, or Diagnostic Starting Point - Engine Controls in Engine Controls - 4.8L, 5.3L, 6.0L, or Diagnostic Starting Point - Engine Controls in Engine Controls - 6.6L, 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 
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