GM Service Manual Online
For 1990-2009 cars only

Perform a localized test for leaks using either water or air. Begin the test at the base of the suspected area. Slowly continue upward until you locate the leak.

Important: 

  1. Pinpoint the leak area before you make any repair. Random repair may only temporarily restrict water entry. This may make future diagnosis and repair more difficult.
  2. Continue localized testing in the same general area in order to confirm that you have located all of the leaks.