A damp carpet or water on floor passenger side situation can be caused by a plugged ac condensate drain line a leaking heater core leaking windshield seal a problem with sunroof drains or water ingestion from the fresh air intake on your car s hvac system.
Water on floor of car back seat.
We first noticed the problem when a friend sat in the back and got a wet bum.
Water will always flow towards the back seat because it sits lower than any other part of the car.
If your floorboards have an inch or more of standing water you ll want to use a wet dry vac to suck it out taking particular care to get into the nooks and crannies between the seats center console and armrests.
Check to see whether the liquid collecting in the car is antifreeze or water don t taste it.
I recommend you check the front carpet under the floor mats and the trunk in the spare tire well and surrounding area for any water or wetness this will indicate where the water is coming from that would be the first step and will prevent you.
Your first order of business is to get as much water out of your car as possible as quickly as you can.
I stripped the interior out and found a pool of water under the rear bench on the right hand side unsurprisingly and the seat foam was pretty wet too.
Another good indication is if the liquid is only collecting on the passenger side where most heater cores are located.
The heater core is like a little radiator which water passes through under the dashboard to heat the cabin.
This car was getting wet on the right hand rear seat behind the driver.
Re seal the barrier and the problem goes away.
The glue sealant that holds that barrier to the door frame can go bad when that happens the water goes inside the car rather than down the drain.