PASSENGER FLOOR IS GETTING WET, WHERE IS THE WATER COMING FROM?, IT DOESN'T SMELL LIKE COOLANT.
Might be the seal on your inner door has failed or the weatherstripping is worn, and or the sunroof drains are clogged,(if you have one).
I am not disagreeing with Tom, only offering another opinion. Which is, your A/C evaporator, the "grille' like thing in the cabin up under the dash, that cools the air when the refrigerant evaporates, chills the air flowing over it, what happens is the evaporator collects moisture and it either freezes on it or just collects the moisture until you shut of the A/C...then is should drain outside the car...... unless the drain hose has become unattached or cracked...hence water on the carpet
I had the same issue. Except I discovered I WAS leaking engine coolant. Dealer "fixed" leak causing passenger floor to become wet. They "fixed" it three times. Also fixed leak in trunk. That one they got right. This other leak just kept coming back. I went through two engine mounts, also, plus a variety of other repairs. I finally just traded it in, after 141,000 miles.
Check/Clean sunroof drains. Clean out behind the back of both front tire wells. Unscrew bolt at the bottom. I found 8 years of backup down there. Hasn't leaked since. Also have to deal with a leaky trunk. Two holes have to be re-patched but must remove the back bumper to access them. I love this car but am not impressed with GM's cheep assembly...
Here is the answer to why your back seat floor is getting wet. I had this problem and to solve it on my own. No excuse for GM not to publicize this. Take the backseat out (Takes two minutes). You will see the battery. The battery has a drain hose going from it - To a hole in the floor board. The problem may be: 1. The hole is clogged 2. The hose is clogged 3. Both Simply clear them and reattach.
Looking for a Used Lucerne in your area?
CarGurus has 2,648 nationwide Lucerne listings starting at $1,848.
Search Buick Lucerne Questions
Buick Lucerne Experts