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Weird Tire Problem-Where's the Leak?

My 2009 Hyundai Sonata has had a strange tire problem almost since it was brand new. (It’s now about 15 months old and has around 13K miles.) The Tire Pressure Monitoring System (TPMS) light comes on frequently. It took me a few tries, but I figured out that it was always one particular tire (front left) that had low pressure-- usually only a few pounds under the recommended pressure. This started happening fairly frequently, and sometimes the pressure was substantially lower than the recommended pressure. (I should note that I don’t drive this car on a daily basis-- maybe once a week, and occasionally on long trips.) Anyway, I took the car in to a tire dealership that also does repairs and they couldn’t find any leak in the tire. They thought it might have something to do with the TPMS and that it could be mistakenly releasing air from the tire when it was measuring the pressure. In any event, they couldn’t fix it. Today I took it to a Hyundai dealership service department (and, coincidentally, the tire was COMPLETELY flat when I went to the car the first thing in the morning.) Before I left, I filled it up with air (like I usually do.) I explained the problem to the dealer, and ended up with the same result. They said there’s nothing wrong with the TPMS, and neither they, nor their tire dealer partner, could find a leak in the tire. I should mention that frequently the tire will stay full for several days or a week, when at other times, it will go flat (or lose pressure) in one day. I’m wondering if it could be self-sealing at times, or if it’s parked a certain way it doesn’t leak. Anyway, I’m totally lost and have no idea what to do next. No one can fix it since they can’t find a problem. I guess I could just buy a new tire, but it seems wrong since the tires are all in good condition otherwise. Any ideas?

First, it is under warranty, have the dealer get you a new tire. Second, the TPMS is only a sensor, it can not inflate or deflate a tire, so do not go back to your tire guy as he has no idea how a TPMS system works. Lastly, it is common for mystery tire leaks to only happen when the hole is on the bottom of the tire and the full weight of the car is on it. One final note, I would rotate that tire to the rear of the car, to make it safer. You do not want a drive wheel to be underinflated.

Since the tire is under warranty make them put the whole wheel in a water tank. The wheel could have a leak in it. If it’s an alloy wheel this is very possible. A water tank will let them know exactly where the leak is. The TPMS is a “monitoring” system only.