GM Service Manual Online
For 1990-2009 cars only
  1. Mask the pressure relief valves.
  2. Close all the windows and doors.
  3. Connect the vehicle ventilation fan to the ON position, with the selector at high speed and in the defrost mode.
  4. Unlock and close the doors.
  5. Apply the soap solution to the potential leak areas.
  6. Look for bubbles. When bubbles escape, there is air escaping.