GM Service Manual Online
For 1990-2009 cars only
  1. Apply the park brake.
  2. Block the vehicle wheels.
  3. Shift the transmission into NEUTRAL.
  4. Start the engine and allow the engine to idle.
  5. Engage the clutch (release the clutch pedal).
  6. Disengage the clutch (depress the clutch pedal): maintain the clutch in the disengaged position for 9 seconds.
  7. While still maintaining the clutch in the disengaged position, shift the transmission into reverse.