I have a leak after heavy rain under passenger side of dashboard. Any ideas as to why I have the leak. Would like to fix myself.
Been There Done This. The Water Could Be Coming Through A Door And Running To The Lowest Area, Powered By Gravity.
A March, 1994 Buick Technical Service Bulletin written for GM technicians explains this probable source of water leaking into the passenger compartment of 1991-1994 Park Avenues, Olds 98s, Olds and 1992-1994 LaSabres, Olds 88s, and Pontiac Bonnevilles.
A few of GM models from this era ( and more recently) had doors that had problems with leaking “door moisture shields” (a large plastic panel behind the interior door trim panel). They are stuck to the door shell with a ribbon type of sealant and would sometimes develop a little “gap” in sealant and leak at the bottom.
Water ordinarily leaks into a door from the window slot. The moisture shield is supposed to channel the water to the bottom of the door where it flows out of vents on the bottom and outside. The leaking shield would allow water to enter the car between the lower edge of the interior trim panel and the door. A person inside with a flashlight can watch for leaks in this location while an assistant floods water from a hose onto the door window. Dabbing with a dry tissue is useful inside to help find the leak.
When the door trim panel is removed you should see evidence where water was leaking. Removing the door trim and resealing the “gap” with butyl sealant (after cleaning surfaces - I’ve used denatured alcohol) takes care of leaks in this location. I got my butyl “ribbon” from an auto glass shop.