Where can you check for a rainwater leak in your 1998 Toyota Sienna that appears on the front floor only does nothave to be moving to get wet and shows no other trace of water anywhere?

If you have a sunroof I had the same problem on our 2001 XLE. It drains through the windshield front frame which gets clogged over time with decayed material ( my wife was parking the car under trees). The water comes in from the sunroof track as it can't drain properly. You have to get the dealer or whoever to blow out the material with compressed air. I saw the gunk come out. Look under the van and you will see the drains. We also had a factory installed wind deflector which I took off.

Answer

You didn't mention whether this was rain-related or not. If it isn't, your air conditioner drain line may be unhooked under your dashboard so your a/c may be draining inside. That happened to me and the floorboard on the front passenger side kept getting wet. After I fixed the drain line the problem was solved.

Answer

I don't buy the AC drain line answer. My Sienna has the same problem, on both sides at the front. The carpets are soaked and smelling like a wet dog after every heavy rain. I read somewhere else that loose or missing air-duct covers may be the culprit for rear rain-water leaks and tend to believe that could be possible for the front too. Another possibility is that the plastic molding that contacts the base of the windshield is missing a bolt and a bit loose on my unit. So I may try to caulk and tighten that (in my infinite spare time of course). Then I will definitely look a bit closer at the Odyssey before my next purchase.

Another viewpoint:

Have you ever been in the car when it was raining and the water was coming in? Where it comes in and when it comes in can make answering your question easier. I have this problem repeatedly with my 2003 Sienna XLE. Water comes in around the sunglass holder, the molding at the roof on both sides and at the molding at the bottom of the door. I have had to bring it in more than once for repair and it is time to bring it in again. In my case, it is the sunroof and the clogged drains. The last time it got so bad that they couldn't blow them clean and had to drill them out (I think they got full of sticky tree sap). Unfortunately, I can't help where I park so I need to bring it in to be cleaned out every 6 months or it becomes a bigger job. They have recommended that I remove the wind deflector in the front of the sunroof to help alleviate the problem, but I stubbornly keep it on.