Find your leak (it may not be the sunroof)

Before taking anything apart, confirm where the water is really coming from. The wet spot you find is usually a destination, not the source.

Found standing water? Do this first

Diagnosis can wait an hour. Wet carpet cannot, and neither can wet electronics. On most cars the control modules, fuse boxes and harness connectors sit low, under seats and behind kick panels, which is exactly where water from a roof leak ends up.

1. Get the water out before you look for where it came from. Lift the floor mats out of the car entirely. A wet-vac on the carpet pulls out far more than towels will.
2. Check the underlay, not just the carpet. The foam under the carpet holds water long after the surface feels dry, and that is what causes the smell and the corrosion. Press a paper towel into it: if it wets through, the padding is still soaked and the carpet needs lifting at the sill to dry properly.
3. Get air moving. Doors open, a fan pointed into the footwell, and a dehumidifier in the car overnight if you have one. Parking in the sun with the windows cracked helps; sealing a wet car up does not.
4. Treat electrical symptoms as urgent. Warning lights, a dead module, seats or windows misbehaving, or an SOS or telematics fault after a wet spell are all signs water has reached a connector. Corrosion continues after the water is gone, so this is the point to stop DIY and get it looked at.
5. Photograph everything while it is wet. If there is a warranty extension, a bulletin or an insurance claim in your future, the wet-carpet photos taken on the day are worth more than a dry car and a description later.

Once the car is dry, come back and work through the checks above to find the source. A car that has been dried but not diagnosed will simply do it again at the next heavy rain.

Start here: three quick checks

These three checks rule the sunroof in or out before you remove a single panel.

1. Rain, or air conditioning?

   If the floor only gets wet when the A/C is running and there is no puddle under the car, the water is almost certainly the air conditioning condensate drain, not the sunroof. It is clean and tracks A/C use, not rain. If the car gets wet after rain or a wash while parked, it is an outside water path, so keep going.

2. Test the sunroof drains

   Pour a cup of water into each corner of the open roof and watch it run out underneath. Watch two things: the water arriving at the outlet underneath, and no water appearing inside. A split or disconnected tube can swallow water at the tray and still leak into the cabin, so a drain that takes water is not proof on its own. See cleaning and testing your drains for the full method.

3. Look at the seal

   Wind noise at speed plus a visible gap where the rubber has pulled back from the glass points to a shrunken seal. That gap also floods the drains with debris, so check the drains too. See caring for your seal.

If it is none of those, trace it

When the drains flow and the seal looks fine, the water is getting in somewhere else. Find it the methodical way:

• Hose one zone at a time with someone watching inside: windshield and cowl first, then the roof and antenna, then each door, then the tailgate. Isolating zones is what tells the sources apart.
• Trace the wet track uphill. Lift the carpet and trim and follow the water back to its highest wet point. If the foam under the carpet is dry but the surface is wet, the water came from above.
• Add dye if it is stubborn. A water-soluble, non-staining leak-tracing dye in the test water, read under a UV light, will show a thin crack you cannot otherwise see. Check the product is safe on fabric and trim before you use it, and rinse afterwards: automotive dyes made for oil or refrigerant will stain a headliner.

Where it is wet, and what that points to

Other leak sources (not the sunroof)

These are the usual impostors, roughly most common first. The detail varies by make, so your vehicle guide lists the specific spots and any bulletins for your car.

• Cowl or plenum drain. Leaves clog the drains at the base of the windshield, and water overflows into the cabin air intake and the front footwell. This is the single most common leak mistaken for the sunroof.
• A/C condensate drain. A blocked evaporator drain spills into the footwell when the A/C runs. Clean water, tied to A/C use, with no puddle under the car.
• Windshield top edge. A failed urethane bond lets water down the A-pillar onto the dash and front floor. A hose test along the top edge, or a close look at the urethane bond, will show it. Do not test it by pushing on the glass.
• Roof antenna base. A cracked antenna seal drips onto electronics in the headliner. It often shows up first as electrical faults (radio, GPS, or SOS warnings) after rain or a wash, with a damp headliner.
• Tail light and rear lamp gaskets. A dried lamp gasket lets water into the trunk or spare wheel well, common on wagons and SUVs where the roof funnels water onto the lamp tops.
• Door vapor barrier. The plastic membrane behind the door card peels at the bottom, so water that should drain out the door gets into the cabin. Usually a wet rear footwell or door sill.
• Liftgate seal and third brake light. On SUVs, a hardened liftgate weatherstrip or a leaking roof-spoiler brake light lets water into the cargo area.
• Body seam sealer. On older cars the factory sealer over welded seams cracks and opens a path along a body seam, often into the trunk floor or spare well.
• Heater core (a mimic, not a leak). A wet footwell with an oily film and a sweet smell is engine coolant, not rainwater. That one is a repair, not a drain to clear.