Hello all i'm new to this forum. I had my S40 for 10 years and with no major problems. I do have one now and it has to do with water under my carpet. It has been going on a while. I've tried and tried to find where it could be coming from and can't pin point. I checked my sunroof drain holes and those were good. I peeled back the carpet towards the middle and saw the A/C drain was not clogged or at least it is still attached. I did blow some compressed air through it. Well which the A/C have been draining on the ground as well. I noticed water coming from out of the vent under the seat. I do have a crack towards the bottom of the windshield that goes all the way across. I'm wondering could that some how cause water to come in? I vacuumed the water from the rear driver and passenger side floor a couple of weeks ago. It rained the last couple of days and i noticed at least an inch of water back in the rear floor again, I'm wondering if the crack in the windshield is the culprit? Also the car is acting very strange won't shut off (about a couple mins. later) when i switch it off, my blower motor keeps running until it kills the battery, so i had to unplug the battery and water is still coming in. I'm thinking all that water got my electrical system messed up. I just don't know where it is coming from. Has anyone else had this issue?

 

Did you check all 4 drain lines for the sunroof?

 

That is exactly what happened to my Volvo s40.Water flooded my entire passenger side floor under seated in back. I never saw anything like it before. I noticed my coolant reservoir empty every time it happened and when I filled it the same thing happened. To stop it temporarily you need to detach the heater hoses that is attached to passenger side wall leading to inside under glove compartment. Once you remove them from wall, connect the two hoses together. The flooding will stop then everything can dry because water got all up in my fuse area. If you go under glove box and pull down the fuse box you will see massive water damage and I figured out why the car was going haywire. my car did the same as yours. The only problem is you can't use the heater, I live in Hawaii so I have no problem without heater.