Recently, I used a faucet with a large amount of water to wash the car, and found that water droplets had fallen onto the foot pad between the co-driver’s glove box and the A-pillar. When inspecting the roof of the car, I found a palm-sized wet spot near the door handle. I finally realized that it was a sunroof problem and finally found the source of the water leakage. Because after washing vehicles once or twice in the past few years, water was found between the glove box and the A-pillar. It was suspected that the water from the steel plate near the drainage hole on the outer side of the A-pillar flowed into the car from there (the first car encountered this problem). I took apart the plastic cover on the rain wiper and checked it with a large amount of water. I didn’t see any water leaking into the car. I didn’t leak when driving on rainy days. I couldn’t find the reason. This problem has troubled me for several years. If the car is flooded, it would be a big problem. This time I was very happy to find the source of the water leakage. I removed the door frame sealing strips, roof handles, sun visors, sunroof controller panel, A-pillar and B-pillar interior trim panels, sunroof opening and roof trim strips on the co-driver’s side. By gently pressing the roof, you can clearly see the hidden drainage system inside the corner of the skylight. Slowly pour water from the roof into the water guide trough. It is found that the drainage holes and water pipes leak quickly, which means that it is not blocked and the water pipe joints are not loose. Leakage, no water seepage is seen in the entire water guide trough. Where does water leak? Later, I sprayed water on the entire sunroof corner and finally saw how the water flowed into the car. It turned out that there was a gap between the sunroof water guide channel and the roof iron sheet, and the roof iron sheet opening at the corner of the sunroof was very high (design flaw?). The sunroof glass of my car is uneven with the roof after it is closed, and it is a little lower than the roof iron. It is not tight and has gaps. I think the water rushed through the two gaps and shot into the car when the water pressure of the car washing was high. There are almost no second possibilities. I plan to improve it and prevent water from flying into the car.